Wiley: Journal of Fish Biology: Table of Contents

DNA extracted from boiled archival fish bones yields high‐quality whole‐genome sequencing data

Thu, 09 Apr 2026 20:32:12 -0700

Abstract

Archival samples provide a unique source of organismal DNA, offering the potential to extend the temporal scale of genetic studies by decades to centuries. Fish hard structures, such as otoliths and scales, serve as records for fish collected during fisheries monitoring across a large spatiotemporal scale. Operculum bones are a type of fish hard structure that, although less commonly collected, have been utilised in genetic studies. However, the potential of archived operculum bones to provide high-quality whole-genome sequence information has not been thoroughly evaluated. Here, we applied a commercially available extraction protocol, with minor adjustments, to isolate genomic DNA from operculum bones of Eurasian perch collected up to 47 years ago, followed by standard next generation short-read whole-genome sequencing. By comparing the metrics of DNA and whole-genome sequencing data of bones with contemporary muscle samples, we demonstrate that the application of a simple extraction protocol on boiled archival fish operculum bones yields high-quality genomic information that is comparable to fresh tissue, highlighting the role of archival operculum bones as an overlooked repository of valuable genomic information.

Labeo kaage sp. nov., a new species of cyprinid fish (Teleostei: Cyprinidae) from the Cauvery River basin, India

Thu, 09 Apr 2026 18:59:38 -0700

Abstract

A new species of Labeo, Labeo kaage, is described from the Cauvery River, India. This distinctive black-coloured species closely resembles Labeo nigrescens, Labeo filiferus, Labeo chekida and Labeo calbasu but is distinguished by unique morphological and genetic traits. It differs from L. nigrescens in the pectoral fin not reaching the pelvic fin, the presence of ½8–½9 + 1 + 6 scales in transverse series, 16½ branched dorsal-fin rays, 37–38 vertebrae and absence of the lateral-line kink near the 17th pored scale. Unlike L. filiferus, the anterior dorsal-fin rays are not filamentous, and prominent acanthoid tubercles are present in the preorbital field. Compared to L. calbasu, L. kaage has a shallower body depth [27.4%–31.8% standard length (SL)], a dorsal-fin base that is longer than its height and the adpressed pelvic fin reaching the anal-fin origin. Mitochondrial cytochrome c oxidase subunit I (COI) gene analysis confirms that L. kaage is genetically distinct, with uncorrected p-distances of 5.4%–6.2% from L. calbasu and 5.2%–5.4% from L. nigrescens. Additionally, L. kaage is distinguished from congeners by its uniformly dark green to black body and fins, the presence of two pairs of barbels longer than the eye diameter, acanthoid tubercles with 3–5 spines in the preorbital, ethmoid, rhinal and rostral fields, a greatest body depth not exceeding one-third of the SL, non-extended anterior dorsal-fin rays, adpressed pectoral fins not reaching the pelvic fins and a lateral line with 38 + 2–3 scales. This discovery underscores the importance of continued exploration to reveal the rich fish diversity of the Cauvery River basin.

Genetic diversity and population structure of the native grass carp (Ctenopharyngodon idella) from the Xiangjiang River revealed by microsatellite markers

Thu, 09 Apr 2026 01:17:12 -0700

Abstract

To investigate the genetic diversity and population structure of native grass carp (Ctenopharyngodon idella) in the Xiangjiang River, 16 highly polymorphic microsatellite markers were selected from the grass carp genome for a population genetic analysis of 300 individuals collected from a single section (Xiangluzhou) of the river, representing six different year-classes (2016–2022). A total of 322 alleles were detected, with fragment sizes ranging from 126 to 314 bp. All 16 loci were highly polymorphic. The six year-classes exhibited high levels of genetic diversity: the number of alleles (N _a) ranged from 12.688 to 16.375 (mean = 14.927), the effective number of alleles (N _e) from 7.160 to 9.115 (mean = 8.239), observed heterozygosity (H _o) from 0.868 to 0.906 (mean = 0.889), expected heterozygosity (H _e) from 0.853 to 0.881 (mean = 0.867), polymorphism information content (PIC) from 0.8367 to 0.8705 (mean = 0.8541) and allelic richness (A _r) from 12.651 to 16.315 (mean = 14.867). Analysis of molecular variance (AMOVA) revealed that 98.19% of the total genetic variation resided within populations, whereas only 1.81% occurred among populations, indicating weak genetic differentiation. Both unweighted pair group method with arithmetic mean (UPGMA) phylogenetic tree and principal coordinate analysis (PCoA) consistently showed a closer genetic relationship between GC2021 and GC2016, and a relatively more distant relationship for GC2017 and GC2022. Structure analysis suggested an optimal clustering at K = 10, revealing an admixed genetic structure with subtle temporal differentiation among year-classes, indicating diverse genetic compositions across cohorts. Bottleneck analysis provided suggestive evidence of historical population size reductions, but no strong signals of recent genetic bottlenecks were detected. Estimates of effective population size (N _E) using the linkage disequilibrium method (the minor allele frequency threshold is 0.02) ranged from 16.9 to 111.3 across year-classes, with a mean of 54.83. Although some year-classes exhibited low N _E values, the high gene flow among cohorts may mitigate associated inbreeding risk. These findings provide a scientific basis for the conservation and sustainable utilization of native Xiangjiang grass carp, with important implications for maintaining aquatic biodiversity in the Xiangjiang River and supporting the development of aquaculture industry.

Air exposure test in Colossoma macropomum juveniles maintained in water at suboptimal temperature: Physiological, metabolic and oxidative stress responses

Wed, 08 Apr 2026 21:58:39 -0700

Abstract

This study evaluated the physiological, metabolic and oxidative responses of Colossoma macropomum subjected to air exposure when maintained in water at suboptimal temperature (23°C). A total of 54 fish (81.33 ± 11.90 g) were distributed into nine tanks (6 fish per tank). For the air exposure test, 24 animals were exposed for 30 min and another 24 animals for 60 min. Six fish from each group were sampled immediately after exposure and at 1, 24 and 48 h post-exposure for blood collection; then they were killed, and the brain, gills, liver and kidneys were obtained for oxidative stress analyses. Air exposure and collection time led to changes in haematological, biochemical, gasometric and electrolytic parameters as well as those in oxidative stress in tissues. The fish modified their physiological parameters when subjected to stress by air exposure for 30 or 60 min, reestablishing baseline conditions at 48 h after air exposure, even when maintained in water at suboptimal temperature.

Age determination in coldwater schizothoracine fishes of the Kashmir Himalaya: Comparative evaluation of otoliths, fin rays and scales

Wed, 08 Apr 2026 21:35:39 -0700

Abstract

Accurate age determination is fundamental to fisheries science, yet the precision of different calcified structures varies significantly across species and environments. This study provides the first comparative assessment of age estimation using whole otoliths, dorsal-fin rays and scales for endemic fish species in the Kashmir Himalaya. We collected 500 specimens of seven species (Schizothorax plagiostomus, Schizothorax niger, Schizothorax labiatus, Schizothorax curvifrons, Schizothorax esocinus, Crossocheilus diplocheilus and Triplophysa spp.) from various lakes and rivers. Age estimates from three independent readers were analysed using intraclass correlation coefficient (ICC), coefficient of variation (CV), paired t-tests and Bland–Altman plots. Whole otoliths consistently provided the most reliable age estimates across all species, with the highest precision and lowest inter-reader variability. Dorsal-fin rays offered a viable non-lethal alternative with moderate precision (e.g. ICC = 0.601–0.701 for S. niger and S. labiatus), whereas scales exhibited the highest variability and poorest reliability, particularly in older fish (CV up to 145% in S. esocinus). Species-specific performance varied, with S. plagiostomus showing the most consistent results across all structures, and S. curvifrons and S. esocinus exhibiting high intra-reader variability. These findings underscore the necessity for structure-specific and species-specific calibration in ageing studies. We recommend otoliths for high-precision demographic studies and fin rays for non-lethal monitoring, providing a critical foundation for developing standardized ageing protocols and sustainable fisheries management in the region.

Integrative taxonomy reveals two new species of whiptail catfishes Loricaria (Siluriformes: Loricariidae) from northeastern Brazil

Wed, 08 Apr 2026 21:11:36 -0700

Abstract

Two new species of whiptail catfish, Loricaria (Siluriformes: Loricariidae), were discovered in the Munim and Itapecuru river basins, Maranhão State, northeastern Brazil, through an integrative taxonomic approach combining morphology and mitochondrial DNA. Linear discriminant analysis revealed three morphometrically distinct groups, and coxI-based phylogeny identified four genetically divergent lineages of Loricaria in northeastern Brazil. The new species are clearly distinguished from their closest congeners, L. turi and L. parnahybae, by unique diagnostic traits, including abdominal plate patterns, pectoral girdle coverage and the shape of the postorbital notch. Genetic divergences among lineages, estimated as mean interspecific K2P distance, ranged from 2.2% to 4.1%, similar thresholds commonly applied for species delimitation in Loricariidae. Both species exhibit restricted distributions and are endemic to river basins under increasing anthropogenic pressure. These results underscore the underestimated diversity of Loricaria in northeastern Brazil and reinforce the role of coastal drainages as areas of endemism and speciation.

Reaching gender parity and improving internationalisation after five decades of FSBI symposia, but subtle career‐stage effects on timekeeping remain

Joshka Kaufmann, William Bernard Perry — Tue, 07 Apr 2026 17:10:13 -0700

Abstract

We analysed 57 years of Fisheries Society of the British Isles (FSBI) symposia, showing speakers with traditionally female names increased from near absence to reaching parity in recent symposia. International affiliations increased in the late 1980s, peaking in 2024 with 27 countries, albeit with overrepresentation of high-income countries. Timekeeping for 68 presentations at the 2025 symposium showed that senior scientists were more likely to overrun than junior presenters; no systematic gender differences were detected. Although gender representation has improved, timekeeping asymmetries reveal career-stage effects, underscoring the need for consistent data collection, moderation and equitable session management.

Climate change linked to infertility in well‐known shark species

William Bernard Perry — Mon, 06 Apr 2026 08:39:22 -0700

Journal of Fish Biology, Volume 108, Issue 2, Page 417-418, February 2026.

Issue Information

Mon, 06 Apr 2026 08:39:22 -0700

Journal of Fish Biology, Volume 108, Issue 2, Page 413-416, February 2026.

Reply to Figueroa‐Muñoz et al.'s comment on ‘multiple tools to investigate the origin of the exotic species Chinook salmon Oncorhynchus tshawytscha (Walbaum, 1792) (Salmonidae) in the world's largest chocked coastal lagoon’

Mon, 06 Apr 2026 08:39:22 -0700

Journal of Fish Biology, Volume 108, Issue 2, Page 419-420, February 2026.

The unicorn ray: a morphological abnormality in a southern eagle ray (Myliobatis tenuicaudatus)

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

We document a unique dorsal protrusion of a southern eagle ray (Myliobatis tenuicaudatus) by-caught in a trawler off the coast of New South Wales, Australia. Radiological imaging led us to conclude the abnormality is a congenital defect that resulted in a pair of additional pelvic fins growing on the dorsal surface. It is unlikely the abnormality had substantial impact on the growth and survival of the animal since it had grown substantially since birth and there was minimal impact to structures that facilitate the movement required to forage and evade predators.

Bite, swab, identify: Validating molecular tools for detecting depredating shark species

Diego Cardeñosa, Phillip A. Grogan, Demian D. Chapman — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Depredation, the partial or complete removal of hooked fish by predators, poses significant challenges for fisheries worldwide. Shark depredation in recreational fisheries has become a growing concern, influencing both fisheries management and public perceptions of shark conservation. Although DNA swabbing of depredated fish has been used to identify responsible shark species, the reliability of this technique remains uncertain due to potential environmental DNA (eDNA) contamination. In this study, we evaluated the accuracy of swab-based molecular identification by comparing genetic results to video-confirmed depredation events. Four depredation events were recorded in Jupiter, Florida, involving a bull shark (Carcharhinus leucas), lemon shark (Negaprion brevirostris), great hammerhead shark (Sphyrna mokarran) and great barracuda (Sphyraena barracuda). DNA analysis of swab samples from depredated fish correctly identified the responsible shark species in all three shark cases. Barracuda depredation yielded no amplification. Our findings validate the use of swab-based molecular techniques for accurately identifying depredating shark species and confirm the absence of misleading eDNA signals. This approach provides a valuable, non-invasive tool for studying predator–prey interactions and informing fisheries management strategies.

On the occurrence of the snakefish Trachinocephalus myops (Aulopiformes: Synodontidae) in the Azores archipelago

Iryna Hulevata, Filipe M. Porteiro, Eva Giacomello, Diana Catarino — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

The snakefish Trachinocephalus myops is an Atlantic species distributed in tropical and temperate coastal waters on sandy substrates. This study reports the validated record of an adult T. myops in the Azores archipelago caught by a fisherman at Faial Island. Meristic, morphometric characters and molecular analyses supported species identity. The possibilities of recurrent misidentification or recent colonization of the species in the region and its biogeographic affinities are discussed. T. myops is hereby included as a native species in the Azores.

Integrated molecular and morphological evidence reveals a new Rhodeus species (Cyprinidae: Acheilognathidae) from the Turkish Aegean basin, with a redescription of Rhodeus meridionalis

Gökhan Kalaycı, Irmak Kurtul, Esra Bayçelebi, Cüneyt Kaya, Davut Turan — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Rhodeus tugbae new sp. is described from some streams and rivers on the Turkish Aegean Sea coast. The new species is distinguished by a slightly sub-inferior mouth, a sharped predorsal keel, a body strongly compressed laterally and 3–4 scale rows between the anal-fin origin and the lateral series. This study contributes to understanding biodiversity and endemism in the freshwater ecosystems of the Aegean region. Rhodeus tugbae was compared to R. amarus and R. meridionalis, distributed in adjacent basin, using principal component analysis (PCA), and the results confirmed that R. tugbae differs from R. amarus and R. meridionalis. R. tugbae sp. nov. differed from its most closely related congener, R. meridionalis, by 14 diagnostic nucleotide substitution sites based on mitochondrial DNA (mtDNA) cyt b sequences. A revised description of R. meridionalis is also included due to the limited diagnostic features in the original description.

Linking rivers, mixing faunas: How artificial connectivity between the Middle and Upper Paraná River basins shapes fish diversity in a tributary of the Itaipu Reservoir, Brazil

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

This work aimed to investigate the distribution and occurrence of fish species along the São Francisco Falso Braço Norte (SFFBN) River basin, a tributary of the Middle Paraná River basin now artificially connected to the Upper Paraná ecoregion, to evaluate how such connectivity may affect the biogeographic distribution and regional composition of freshwater fish species. Quarterly samplings were conducted between August 2022 and May 2023 at 12 sampling points distributed along the longitudinal axis of the basin. The fish were collected using sieves, casts, seines and gillnets. The results suggest that, although the SFFBN River basin is currently integrated into the Upper Paraná ecoregion and strongly influenced by the dynamics of the Itaipu Reservoir, its fish community still harbours species likely linked to the biogeographic history of the Middle Paraná River basin. These species, particularly in the middle and upper stretches of the SFFBN River basin, appear to have persisted without being directly affected by the damming. Therefore, monitoring the fish community in Itaipu's tributaries is essential for understanding the impacts of ongoing ichthyofaunal homogenization between the Lower and Upper Paraná ecoregions.

Change of micronucleus frequencies, antioxidant parameters and in silico in carp (Cyprinus carpio) fry exposed to ibuprofen

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Ibuprofen, a non-steroidal anti-inflammatory drug, has been detected in the aquatic environment, but little is known about its effects on fish and other aquatic organisms. This study aimed to investigate the effect of ibuprofen on micronucleus levels in erythrocytes and whole-body antioxidant parameters of carp (Cyprinus carpio) fry. Fish were exposed to immersion in two different doses of ibuprofen concentrations (50 and 250 μg/L) for 24, 48, 72 and 96 h and 14 days. No mortalities occurred in any group during the test. Abnormal behaviours such as irregular swimming, loss of balance and hanging vertically in the water were observed in some fish exposed to acute toxicity. In this study, a significant increase in the micronucleus number of red blood cells was observed throughout the study period (p < 0.05). Antioxidant parameters were measured spectrophotometrically. Results obtained showed that ibuprofen significantly increased (p < 0.05) malondialdehyde (MDA) levels, glutathione S-transferase (GST) and catalase (CAT) activities, but decreased (p < 0.05) the glutathione (GSH) levels of whole-body carp fry in a dose-dependent manner. Furthermore, ibuprofen significantly increased MDA, GST and CAT levels, but increased the GSH levels of whole-body carp fry in a time-dependent manner. These results indicate that carp fry is sensible to human pharmaceutical agents in aquatic environments. The manner and the constructed interactions between ibuprofen and two protein targets (immunoglobin and haemoglobin) were investigated using molecular docking and molecular dynamics simulation. The results indicated that ibuprofen could affect the haemoglobin activity. Finally, absorption, distribution, metabolism, excretion and toxicity analysis was performed to examine the drug potential of the studied molecules.

Spectral characteristics of visual pigments in two mullet species (Pisces, Mugilidae)

Sergei L. Kondrashev, Nina E. Lamash — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

The spectral properties of photoreceptors in two closely related fish species of the family Mugilidae, differing in their preferred salinity habitat, were subjected to a comparative study using microspectrophotometry and liquid chromatography. The results have shown that both species are tetrachromats and possess two classes of single cones and two classes of double cones, with paired elements containing visual pigments with the same absorption maximum (λ _max). In the flathead grey mullet (Mugil cephalus), a predominantly marine species, the rods and the single (two classes) and double cones (two classes) contain rhodopsins with λ _max = 506, 464, 518, 560 and 574 nm, respectively. In the so-iuy mullet (Planiliza haematocheilus), with a freshwater life-history stage, the photoreceptors contain a mixture of rhodopsin and porphyropsin in different proportions. In different P. haematocheilus individuals, values of λ _max of the rods and the single and double cones vary in the following ranges: 501–522, 462–470, 518–539, 573 and 570–620 nm, respectively. The set of visual pigments indicates the identity of opsins in both species, whereas the long-wave shift in the spectral sensitivity in P. haematocheilus is due to a changed composition of the pigment mixture with a greater proportion of porphyropsin that utilizes the same opsins as in M. cephalus. The conclusion about the consistency of our results with the previously found correlation between the supposed connections of horizontal retinal cells and individual chromatic classes of photoreceptors in mullets is made based on literature data. The present study, in combination with studies on the molecular genetics structure of photopigments, can contribute to further development of views on the evolution of visual pigments.

Comparative transcriptome analysis reveals potential candidate genes for resistance to Edwardsiella tarda in turbot (Scophthalmus maximus)

Guanzheng Lyu, Ding Lyu, Yulong Hu, Weiji Wang — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Turbot (Scophthalmus maximus) is one of the most important marine aquaculture species worldwide. However, with the continuous expansion of farming scale, disease outbreaks have become a major constraint to the development of the industry. Among the pathogens, Edwardsiella tarda is recognized as one of the primary causative agents. Identifying resistance-related genes and applying marker-assisted selection present promising strategies for breeding E. tarda-resistant turbot strains. In this study, two families with the highest and lowest average breeding values were selected as resistant and susceptible groups, respectively. Transcriptomic analyses were conducted on spleen and head kidney tissues before and after E. tarda infection. The objective was to identify key genes associated with resistance to E. tarda in turbot. Among all comparison groups, the highest number of differentially expressed genes (DEGs) was observed in spleen tissue from sensitive families before and after infection (NiS vs. InS), with 866 significant DEGs. In contrast, the resistant group (NiR vs. InR) exhibited the fewest DEGs, with only 290 identified. Based on GO annotation and KEGG pathway enrichment, 26 significant DEGs were identified, including 7 upregulated genes (gdf10a, tnfsf12, tat) and 19 downregulated genes (jun, relb, fosab). In the KEGG pathway enrichment analysis, significant enrichment was observed in immune-related pathways, including the MAPK signalling pathway, cytokine-cytokine receptor interaction, toll-like receptor signalling pathway, as well as metabolic pathways such as starch and sucrose metabolism, glycolysis/gluconeogenesis and phenylalanine metabolism. Further analysis revealed that 21 of these genes were enriched in the MAPK signalling pathway and cytokine–cytokine receptor interaction pathway, both of which are closely related to immune and inflammatory responses in fish. To verify the reliability of transcriptome data, four genes (egfra, fosab, gdf10a and si_ch211-79 m20.1) were selected for real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) validation. The results showed consistent expression trends with transcriptomic data, confirming the credibility of the identified DEGs. In conclusion, this study identified several candidate genes associated with resistance to E. tarda in turbot, enhancing our understanding of its immune response mechanisms and providing a theoretical basis for future genetic selection and molecular breeding efforts.

Reproduction and embryonic development of monkeyface prickleback Cebidichthys violaceus in captivity

Kevin D. Hinterman, Matthew R. Hoehn, Luke D. Gardner, Scott L. Hamilton — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Understanding the sequence of embryonic and larval development and the factors necessary to induce reproduction in captivity are critical for developing new species for commercial or conservation aquaculture. In this study, we describe the adult reproductive behaviours and development of eggs, embryos and early larvae of captive monkeyface pricklebacks, Cebidicthys violaceus, compared to previously documented wild observations. Eggs were laid in cohesive clutches and guarded by the male parent until hatching began 23 days post fertilization at 13°C. Fertilized eggs were spherical, approximately 1.5 mm in diameter, covered in an opaque chorion, and contained six adhesive pads around the outside. We characterized the rate of depletion of yolk and the oil globule and growth of the embryo from fertilization until hatching. Notable embryonic stages were documented, including the timing of the first heartbeat, and the development of otoliths, intestinal tract, eye pigmentation, mouth, fins and the circulatory system. Larval length at hatching was about 7.4 mm, and larvae were immediately mobile and feeding on live food. Larvae were cultured and observed up to 18 days post hatch.

On the conflict between science and ethics: the case of the moggel, Labeo umbratus (Teleostei: Cyprinidae) from South Africa

Mpho Ramoejane, Fatah Zarei, Xiluva Mathebula, Albert Chakona — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Recent molecular evidence showed that Labeo umbratus comprises two allopatrically distributed genetic lineages, a northern lineage confined to the Orange-Vaal River system where this species was originally described and a southern lineage with three geographically separated haplogroups (western, central and eastern) distributed across multiple isolated southward-draining river systems in the Cape Fold, Amatola-Winterberg Highlands, and the Southern Temperate Highveld freshwater ecoregions of South Africa. Detailed morphological examination supported recognition of the eastern haplogroup, distributed from the Sundays to the Nahoon River system, as a distinct species. Although a name proposed in 1861 exists for this haplogroup, originally described from the Kat River, a branch of the Great Fish River system, it is derogatory and offensive to the indigenous people of South Africa and has not been adopted in subsequent taxonomic literature. We see no nomenclatural stability in resurrecting a name that is both offensive and long forgotten, and we argue that retaining such a name undermines universality because it conflicts with ethical and cultural acceptance in the region of endemism. Accordingly, we reject the use of this derogatory name and instead provide a new name, Labeo ngqikai, for the species to ensure both nomenclatural stability and cultural sensitivity. The epithet ngqikai honours King Ngqika, the third paramount chief of the native inhabitants of the Kat River valley, from where the species was originally described.

Phenotypic characteristics of hybrid F1 of Opsariichthys bidens (♀) × Zacco acanthogenys (♂) and its embryonic, larva–juvenile metamorphosis development

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

In the present study, an intergeneric cross was conducted between Opsariichthys bidens (♀) and Zacco acanthogenys (♂);the morphological characteristics of the hybrid offspring generation (F₁) were observed and recorded at various periods of the development of the embryos and young larvae; and comparative analyses of the external morphological data of the adult fish and the parameters of their external shape framework were carried out. Results demonstrated that hybrid fertilized eggs maintained at (25 ± 1)°C water temperature completed hatching within 42 h 47 min post-fertilization, requiring an accumulated temperature of 1026.72°C·h. Embryonic development consisted of 7 distinct phases subdivided into 28 developmental stages. Newly hatched larvae exhibited a mean total length (TL) of 5.23 ± 0.06 mm, with complete yolk-sac absorption occurring by 7 days post-hatching (dph). Early developmental growth patterns (0–30 dph) conformed to the quadratic equation: y = 0.02096x ² + 0.23443x + 5.6249 (R ² = 0.9559), where y represents TL (mm) and x denotes days post-hatching. Morphological analysis revealed that meristic traits of hybrid progeny predominantly aligned with the maternal lineage, whereas morphometric ratios exhibited intermediate values between parental species. Principal component analysis and cluster analysis of morphometric proportions and framework parameters demonstrated closer similarity to maternal characteristics. Linear discriminant analysis confirmed distinct phenotypic differentiation among the three groups (parental species and hybrids).

Proteomic analysis of the zone of degeneration at the mitosis–meiosis transition stage in wild‐caught male catshark (Scyliorhinus canicula), correlated with an unusually high‐water temperature in the English Channel

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

In the context of current global change, variations in water temperature are one of the environmental conditions with serious consequences for marine life, including reproductive processes. In the small spotted catshark Scyliorhinus canicula, spermatogenesis occurs in spermatocysts composed of synchronously developing germ cells associated with Sertoli cells, forming a zonal arrangement of the spermatogenic wave. Male catsharks are known to show little to no seasonal variation in spermatogenesis, unlike other sharks that may have a seasonal break at the spermatogonia–primary spermatocyte transition, creating a zone of degeneration (ZD). Unexpectedly, an unusually high number of male catsharks, collected in the eastern English Channel in September 2022, exhibited a ZD. Analysis of bottom water temperatures indicated that the warmest period, from July to September 2022, was higher than the average for previous years. To further explore the biological perturbations associated with the ZD of the testis, a histological description and a comparative proteomic analysis of the ZD with a zone of intact mitosis–meiosis transition were performed. The results showed that only the spermatogonia at stages II to IV were degenerating, as well as their associated Sertoli cells, while the rest of the testicular tissue appeared not impacted. This spermatogonia-specific degeneration was also supported by the proteomic analysis, which showed that only 20% (1565 proteins) of the identified proteins presented a change in abundance. Based on functional annotations, the comparative proteomic analysis revealed cell cycle disruption, impaired DNA damage repair, apoptosis and stimulated lipid metabolism. In addition, follicle-stimulating hormone and luteinizing hormone receptors were upregulated in the ZD. In conclusion, the results showed a correlation between high water temperatures and an arrest of spermatogenesis in S. canicula, with implications for the conservation of elasmobranchs.

Too hot for comfort: Elevated temperatures influence gene expression and exceed thermal tolerance of bigmouth shiners, Ericymba dorsalis

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Environmental and associated ecosystem change may affect the persistence of fish species based on their ability to adapt to changing conditions, including decreasing flows and rising water temperatures. Exceeding the thermal tolerances of stream fish will likely result in a loss of ability to maintain metabolic processes. We evaluated the critical thermal maximum (CTmax) of bigmouth shiner (Ericymba dorsalis) and analysed the expression of heat shock protein 70 messenger RNA (mRNA) (HSP70) to quantify a thermal stress response over a gradient of temperatures (25°C–31°C). E. dorsalis HSP70 mRNA expression was upregulated in response to temperatures >25°C, indicating a stress response. This study supports the existence of a thermal stress threshold for E. dorsalis. The frequency at which this threshold is exceeded may increase under forecasted future climate scenarios for Nebraska.

Batasio eugenius, a new catfish from the Irrawaddy River drainage (Siluriformes: Bagridae)

Heok Hee Ng — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

This study describes a new species of bagrid catfish, Batasio eugenius, from the upper Irrawaddy River drainage in Myanmar. Batasio eugenius is chiefly diagnosed from congeners by its short snout (32–33% head length [HL]), large eye (29–33% HL), very long nasal barbel reaching beyond posterior orbital margin and short adipose-fin base of about 13% standard length, in addition to a suite of other morphological characters. The taxonomic status of B. flavus is discussed and evidence is presented here to show that B. flavus is conspecific with B. travancoria.

Lentipes ptasan, a new species of sicydiine goby (Teleostei: Gobioidei) from the Western Pacific, with a redescription of L. mindanaoensis

Wei‐Cheng Jhuang, Cleto L. Nañola Jr., Xiao Fei Li, Te‐Yu Liao — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Lentipes ptasan sp. nov. is described based on specimens collected from Taiwan and Mindanao Island. It is a large-sized Lentipes species distinguished by several male-specific characteristics, including an upper lip protruding beyond snout obviously, fewer premaxillary tricuspid teeth, two black lines running from the front of the eye through the nostrils to the tip of the snout, a wide brown longitudinal band at the base of the anal fin, and the distinctive nuptial coloration featuring a brown vertical band extending from back to belly on the middle of the body. The complex distribution of Lentipes species and their genetic differentiation may be influenced by sexual selection, historical biogeographic events and contemporary ecological processes. However, due to the recent divergence of Lentipes species, 11 out of 14 species could not be distinguished by the cytochrome oxidase subunit I gene. Furthermore, Lentipes mindanaoensis is redescribed, with L. adelphizonus treated as its junior synonym.

Distribution of some endocrine cells in the digestive tract of Van fish (Alburnus tarichi Güldenstädt, 1814) during reproductive migration

Burcu Ergöz Azizoğlu, Ahmet Regaib Oğuz — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

The Van fish (Alburnus tarichi Güldenstädt, 1814) is an endemic species of the Lake Van basin, belonging to the Cyprinidae family and exhibiting an anadromous life cycle. Although feeding and growth occur in Lake Van, spawning takes place in freshwater streams entering the lake between April and July, influenced by water temperature. These distinct habitats lead to differences in feeding behaviour and nutritional intake. Fish obtain a limited amount of food from the fresh water in which they breed. This study aimed to characterize the distribution of endocrine cells in the digestive tract of Van fish through morphologic, histologic and immunohistochemical analysis, providing insights into the species' digestive physiology. At the end of the oesophagus, there was a stomach-like structure that served as the stomach. In the continuation of this structure, the anterior and posterior intestines were seen. Although taste buds were observed in the mucosa layer of the oesophagus of fish in the lake environment, no taste buds were found in the oesophagus of fish in the freshwater environment. Immunohistochemical analysis identified gastrin (GAS), cholecystokinin (CCK) and somatostatin (SST) cells within the digestive tract. In freshwater fish, GAS and CCK cells did not react in the oesophagus, whereas in lake fish, GAS, CCK and SST were all detected along the tract. The density and localization of these cells differed based on the parts of the digestive tract and the aquatic areas sampled. The distribution of endocrine cells in the digestive tract of Van fish is influenced by feeding conditions, water physicochemical properties and environmental stress, highlighting the adaptive digestive physiology of this endemic species.

Effects of dietary serine addition to a high plant protein diet on growth performance, body composition, hepatosomatic histological structure and metabolism of taurine synthesis in juvenile turbot (Scophthalmus maximus L.)

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

A feeding trial was carried out to investigate the effects of dietary serine on feeding, growth, biochemistry composition, hepatosomatic histological structure and metabolism of taurine synthesis in turbot (Scophthalmus maximus L.) (2.0 ± 0.01 g) fed plant protein-based diets. A fishmeal-based control diet (DietFM) and another two isonitrogenous and isolipidic plant-based diets containing 0.0% (DietPP) and 3.0% (DietS-3%) serine were formulated and fed twice daily (06:30 and 18:30) to fish in triplicate groups for 9 weeks. Feed intake in fish fed DietS-3% was notably higher than that in fish fed DietPP (p < 0.05), and no significant difference was discovered between fish fed DietFM and fish fed DietS-3% (p > 0.05). No significant difference (p > 0.05) was found with the increase of dietary serine in final body weight, specific growth rate, weight gain rate, feed efficiency ratio, protein efficiency ratio and survival rate when a significant increase (p < 0.05) was detected in hepatosomatic index between fish fed DietFM and fish fed DietS-3%. A significant increase was detected from 0.0% to 3.0% serine inclusion in ash content (p < 0.05) when no significant difference was discovered between the DietPP group and the DietS-3% group in moisture, protein and lipid content (p > 0.05). A significant increase (p < 0.05) was found from 0.0% to 3.0% serine supplementation in diets in body tarinre content when hepatosomatic L-cysteinesulphinate decarboxylase activity, cysteamine dioxygenase activity, liver and serum taurine content (p > 0.05) in fish fed DietS-3% showed no obvious difference with those of fish fed DietPP (p > 0.05). The cellular morphology and cell stripes in liver of fish fed diets with 3% serine inclusion were closer to that of fish fed DietFM. Considering the results, 3% serine supplementation in a high plant protein diet significantly increased feeding, mineral accumulation, body taurine content of turbot and obviously improved hepatosomatic histological structure. It is inferred that serine in a taurine-deficient diet can probably convert to taurine to some degree in juvenile turbot, and the transformation differs with tissue distinction.

First attempt at using a synthetic diet in short‐lived killifish, a vertebrate model of ageing

Jakub Žák, Milan Vrtílek — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Diet standardization of model organisms is crucial for experimental consistency and repeatability in laboratory research, yet laboratory fish often lack species-specific, open-formula standardized diets. This study aims to address this gap by testing the effect of macronutrient content on the performance of Nothobranchius furzeri, an intensively studied research model in biogerontology, and providing the basal formula of the purified diet for further development to support the good and consistent performance of this species in laboratory research. After 5 months of feeding, growth, body condition, reproduction and feed efficiency were compared among treatments of individually housed fish fed by one of the two purified diets, (1) high protein (~66% protein, 9% lipid) and (2) low protein (34% protein, 22% lipid), and control bloodworm-fed fish. Survival on both purified diets and male growth on the high-protein diet were comparable to that of the control. The absolute protein intake regulated fish growth irrespective of the total caloric intake. Only the low-protein diet with 22% lipids supported a comparable fertilization rate to the control group. Female performance exhibited greater diet dependency than that of males. This suggests that a female-specific formula should be developed in the future, as males would perform well on a wider variety of diets. This study provides the first data on the performance of N. furzeri fed with a purified diet and establishes a baseline diet formula for further refinement of a standardized laboratory diet for N. furzeri.

Bull trout (Salvelinus confluentus) exhibit binge‐feeding and digestive flexibility during seasonal resource pulses associated with salmon migrations

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Resource pulses are infrequent, ephemeral events of resource hyperabundance that can represent important feeding opportunities for consumers. To capitalize on pulsed resources, consumers can exhibit behavioural and physiological traits including binge-feeding and phenotypic plasticity of digestive physiology, although expression of these traits has not been observed simultaneously. Further, past studies of binge-feeding have largely focused on times and locations where resources were highly concentrated, ignoring potential temporal and spatial variation in consumer responses. We investigated these traits in bull trout Salvelinus confluentus that experience seasonal resource pulses associated with the spring migration of sockeye salmon Oncorhynchus nerka smolts and their fall spawning migrations in a large lake–river system. We also examined spatial variation in S. confluentus diet and feeding behaviour within seasons to explore associations with proximity to aggregated salmon. To do this, we collected S. confluentus stomach contents and analysed consumption rates across seasons and capture locations. We also investigated if the size of digestive organs changed with season. In the spring and fall, S. confluentus consumed O. nerka smolts and eggs, respectively, at high rates, with consumption often exceeding theoretical daily maximums by up to 21.50-fold in the spring and 7.69-fold in the fall. The degree of binge-feeding was correlated with proximity to the lake outlet where smolts and spawning salmon congregate, increasing by 1.21-fold in the spring and 2.78-fold in the late fall for each ~13-km shift in capture location towards the outlet. Salvelinus confluentus also exhibited larger digestive organs during the spring and fall, while the same organs were atrophied during the summer. Our results indicate that a single consumer population can exhibit both behavioural and physiological responses to resource pulses, and that exploitation can vary along a spatial gradient of presumed resource availability. These responses emphasize the importance of resource pulses to consumers and the potential for intra-population differences in consumer responses to transient feeding opportunities.

Community science datasets identify the spatial occurrence and hotspots of flapper skate (Dipturus intermedius)

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

The flapper skate, Dipturus intermedius (Parnell, 1837), is a large-bodied, slow-growing and late-maturing, Critically Endangered elasmobranch with a constrained population distribution. Here, we use two longitudinal community science datasets to investigate the occurrence of flapper skates in Irish waters. The two datasets are as follows: the Inland Fisheries Ireland mark-recapture tagging programme (1972–2021; n records = 1188) and Irish Specimen Fish Committee records (1958–2022, n records = 489). Of the 1677 records, 767 were identified as mature based on size-based thresholds (n males = 418, n females = 349). Hotspots of immature and mature individuals were identified across the south, southwest, north and northwest coasts of Ireland. Flapper skates were predominantly caught within 12 NM of the coast in the summer to early autumn (June–October). Time at liberty ranged from 0 to 11.5 years [mean years ± standard deviation (SD) = 1.5 ± 1.6]. Recapture events were typically <50 km from their initial capture location (93% of individuals), with dispersal distances of up to 171 km recorded. This study demonstrates that mature female and male flapper skate, and immature female flapper skate exhibit interannual site fidelity with short dispersal distances and move within existing ICES stock management areas.

Fission or fusion: shoaling adaptations in green chromides (Etroplus suratensis) across multiple manipulations

Chena Desai, Dinesh Nariani, Rudrik Dave, Ratna Ghosal — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Collective behaviour contributes towards increased fitness. However, in fission-fusion societies, the decision to participate in a group is based on the cost–benefit ratio derived under a given condition. In today's world, this ratio dramatically changes due to increased challenges in degraded habitats, impacting behavioural decisions towards social grouping. In this paper, we used fish shoal as a unit of collective behaviour and investigated variations in shoaling adaptations across a range of manipulations, mimicking challenges faced by the species under natural conditions. We used green chromides (Etroplus suratensis), a cichlid fish species, and characterized their shoaling behaviour under laboratory conditions for two group sizes, 4 and 8. We then examined the effects of different manipulations, for example food-deprivation and reduced space (both mimicking resource constrained conditions), and the presence of hetero species, including tilapia (Oreochromis spp., an alien species widespread within the habitats of E. suratensis), on their shoaling behaviour. Our results showed that E. suratensis formed shoals in both group sizes, 4 and 8. In subsequent analyses, we used group size 8 as a control and demonstrated that space reduction and food deprivation significantly impacted shoaling, reducing shoal splits and occurrences of solitary fish, while increasing incidences of single, cohesive shoals comprising all individuals. E. suratensis also formed mixed-species shoals with alien Oreochromis spp., but exhibited a large percentage (in absolute terms) of shoal splits. Overall, E. suratensis exhibited plasticity in their shoaling behaviour and increased fusion of shoals under challenging conditions, which was in contrast to showing more fission in the presence of the alien species.

Resource partitioning among algal turf‐feeding fishes on a tropical artificial shoreline

Daisuke Taira, Hannah H. J. Yeo, Peter A. Todd — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Rapid coastal development has led to the proliferation of artificial structures along urban shorelines. Numerous studies have shown that patterns of fish diversity associated with these novel habitats are driven by physical habitat complexity; however, trophic-mediated processes in shaping these patterns remain poorly understood. Foraging behaviour and resource partitioning are key strategies that explain habitat use and co-occurrence of ecologically similar species. In tropical artificial shorelines, algal turfs dominate the benthic assemblages and provide a variety of dietary sources (e.g., algae, detritus, microbes, small invertebrates) for multiple trophic groups of fishes. Using carbon and nitrogen stable isotopes, we investigated the trophic niches of 13 common algal turf-feeding fish species on a granite rip-rap seawall in Singapore. We first compared diet compositions among these species by using hierarchical Bayesian mixing models, incorporating prior diet data from gut content and the literature. We then computed ellipse areas based on carbon and nitrogen isotope signatures to compare isotopic niche size as well as ‘typical’ (40% of data) and ‘total’ (95% of data) niche overlaps among these species. Our results revealed varying diet compositions and trophic niche sizes among species, while clear separations in ‘typical’ niche despite significant overlaps in ‘total’ niche among some species indicate resource partitioning. Our findings underscore the role of trophic-mediated mechanisms in shaping seawall fish assemblage patterns and the importance of algal turfs as vital food resources that facilitate fish species co-occurrence.

Filling the gap in current knowledge of basic haematology of chimaeras – the case of wild‐caught American elephantfish Callorhinchus callorynchus

Franco Cristiani, Cynthia A. Awruch, Juan Pablo Barriga, María G. Palacios — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Haematological parameters have become important tools for monitoring natural changes as well as anthropogenic impacts on wild populations of fish. However, for holocephalans, we still have major gaps to fill regarding basic aspects of their haematology. We present the first detailed description of peripheral blood cells of the chimaera American elephantfish Callorhinchus callorynchus together with data on haematological parameters routinely used in animal health assessment. Adults of both sexes (n = 10) were captured in an area with low anthropogenic impact, a gulf in northeastern Patagonia, Argentina. Five major leukocyte types were identified and quantified: lymphocytes (63.33%), heterophils (18.82%), eosinophils (9.8%), neutrophils (4.47%) and monocytes (2.02%). No data on differential leukocyte counts were found for any other free-living holocephalan; however, comparison with values reported for the spotted ratfish Hydrolagus colliei in an aquarium environment showed marked differences. Immature erythroid precursors were regularly found in the peripheral blood of C. callorynchus, whereas no basophils or granulated thrombocytes were observed. Haematocrit values were higher in males than in females. The mean haematocrit for both sexes together was similar to values for its congener the ghost shark Callorhinchus milii and other chimaeras, resembling haematocrits of the least active elasmobranchs, but was relatively low compared to teleost fishes. Our study contributes to the comparative haematology of fishes by including novel information on a free-living holocephalan and starts a dataset of baseline haematological parameters for future studies assessing health status in the context of conservation physiology.

Morphological and molecular evidence reveals a new species of Characidium from the Ucayali‐Urubamba Piedmont, Peru, and novel molecular clades are proposed within the genus

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

A new species of Characidium is described from the Urubamba River basin, within the Ucayali-Urubamba Piedmont ecoregion, Peru. The new species can be readily distinguished from all congeners, except Characidium cacah, Characidium chicoi, Characidium helmeri, Characidium mirim, Characidium nana, Characidium nupelia, Characidium sterbai, Characidium stigmosum and Characidium xavante by the possession of an incomplete lateral line and the lack of an adipose fin. It differs from these species, and remaining congeners, by a unique sexually dimorphic colour pattern: females exhibit irregular dark blotches along the dorsum that alternate elongation between the sides of the body and are usually disconnected from the lateral bars, whereas in males the dark bars are absent. Additional diagnostic features include two series of dentary teeth, absence of a dark blotch on the caudal peduncle, 12 circumpeduncular scales and a fully scaled isthmus. Molecular data indicate a significant genetic divergence between the new species and its closest relatives, further confirming its recognition as a distinct species. Additionally, two new clades were recovered in molecular phylogeny, each formed mostly by species not previously included in any molecular phylogenetic studies.

Monthly differences in the movement ecology of lake whitefish (Coregonus clupeaformis) in eastern Lake Ontario

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Lake whitefish are a cold-water species that holds cultural and economic importance throughout the Great Lakes region. Anthropogenic stressors over the last 60 years (e.g., invasive species, habitat degradation, and pollution) have caused significant declines in their populations. Furthermore, there is limited knowledge on the spatial ecology and habitat use of the species in Lake Ontario. Therefore, we used acoustic telemetry to quantify horizontal and vertical habitat use by lake whitefish over a 3-year period (2021–2024) in Lake Ontario. We also evaluated seasonal changes in bottom-oriented versus suspended behaviours. Lake whitefish were heavily concentrated along the central Duck–Galloo Ridge and in 20–30 m during periods of stratification (June to September), while their distribution shifted to the south shore of Prince Edward County and 10–25 m during isothermal conditions (non-stratified; October to May) and for spawning. During the isothermal period, lake whitefish exhibited a predominantly bottom-oriented behaviour; during stratification, they exhibited both suspended and bottom-oriented behaviours. These differences in vertical and horizontal distribution may be driven by changes in thermal habitats and/or prey; however, further exploration is needed. Ongoing ecological change may influence lake whitefish distribution and behaviours, necessitating changes to monitoring and/or management that accounts for observed behaviours.

Redescription of Enteromius eutaenia (Boulenger, 1904) (Cyprinidae, Smiliogastrinae) and the description of two new species of Enteromius from the Cunene River, southern Africa

Gernot K. Englmaier, Rupert A. Collins, Paul H. Skelton, Martinus Scheepers — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

The orangefin barb, Enteromius eutaenia – a small-sized smiliogastrin barb characterised by orange/yellow fins, a thickened and serrated last unbranched dorsal-fin ray, a dark mid-lateral stripe and a sheath of enlarged scales at the base of dorsal fin – is considered widely distributed across southern Africa. Distinct phenotypic groups suggest unrecognised species-level diversity, but taxonomic progress has been limited by the poor knowledge of true E. eutaenia. Here, we re-examine the type specimens of E. eutaenia and a collection of E. eutaenia-like fishes from the Cunene River system to clarify their taxonomic status, using morphometric/meristic data and mitochondrial cytochrome c oxidase I (COI) sequences. Based on these data, we redescribe E. eutaenia and describe two new species: Enteromius bieensis sp. nov. (found in sympatry with E. eutaenia in the Upper Cunene River close to Huambo, situated on the Bié Plateau, Angola) and Enteromius ruacanaensis sp. nov. (found in the Lower Cunene River, Ruacana Gorge, below the Ruacana Falls at the border between Namibia and Angola).

Spatial habitat partitioning enables coexistence of three Gobiidae species in estuarine environments

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

This study examines resource partitioning (feeding morphology, diet and habitat partitioning) among three gobiid species, the Knysna sandgoby Psammogobius knysnaensis, the prison goby Caffrogobius gilchristi and the river goby Glossogobius callidus, within an estuarine environment. The findings revealed distinct habitat preferences: P. knysnaensis predominantly occupied the sandy mouth of the estuary, C. gilchristi favoured the lower reaches and G. callidus was abundant in the upper reaches. Principal component analysis of feeding morphological traits indicated significant overlap between the feeding morphology of C. gilchristi and G. callidus. Although the two species showed overlapping morphological traits, they exhibited distinct diets, influenced by differences in prey availability within their feeding environments. Cyclopoids, which were widespread throughout the estuary, were a common dietary item for both species. Psammogobius knysnaensis and C. gilchristi had overlapping diets, but each species appeared to dominate in different habitats. This study highlights that habitat partitioning drives resource partitioning among the three species, enabling their coexistence in a dynamic estuarine ecosystem.

Growth and age differences between two male alternative reproductive tactics in the plainfin midshipman

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

The plainfin midshipman (Porichthys notatus Girard, 1854) is a toadfish with two distinct reproductive male tactics: ‘guarder males’ and ‘sneaker males’. These two tactics are anatomically, physiologically and behaviourally distinct from one another at sexual maturity, but it remained unclear whether these two male types remain fixed or plastically transition from one to another across a lifetime. To examine this question, we aged the sagittal otoliths (inner ear bones) of 371 adult plainfin midshipman via the break-and-burn method. Our study showed that guarder males were on average larger and older (mean age: 7.0 years, range: 3–17) than sneaker males (mean age: 3.4 years, range: 2–8) and females (mean age: 5.1 years, range: 2–10). There was considerable overlap in age between guarder and sneaker males; the two tactics were of similar body sizes at age 3, but after that guarder males were always bigger. We used a two-factor von Bertalanffy growth functions (VBGFs) to show that males versus females and guarder versus sneaker males had divergent growth trajectories. The VBGF estimates and distance measures from the otolith centre to the first annual otolith mark suggest that sneakers initially grew more quickly. Our results support the hypothesis that the two male reproductive tactics in plainfin midshipman likely represent distinct fixed life-history pathways that differ early in their development.

Inshore marine coastal zone migration patterns in Atlantic salmon post‐smolts emigrating from eight rivers in north‐east Scotland

Mon, 06 Apr 2026 08:39:22 -0700

Abstract

Atlantic salmon, Salmo salar, migrate through multiple habitat types, each having the potential to impact differently upon migration success. The inshore marine coastal zone is arguably disproportionately impacted by potential stressors on populations. We investigated the migration of Atlantic salmon post-smolts (n = 898) from eight rivers (populations) through the inshore marine coastal zone over a 2-year period using acoustic telemetry. Migration success through marine inlets where fish first entered seawater, and through the wider inshore marine coastal area (the Moray Firth, north-east Scotland) was consistently high across populations and across years (mean = 77%). There was no evidence of the high inshore marine predation rates reported elsewhere. Post-smolts utilised well-defined inshore marine migration pathways that were broadly consistent among populations and over time. The pace of migration through the inshore marine coastal habitat was also consistently rapid across populations and time, with the period of migration being seasonally constrained (mean across population = 36.5; range 18–45 days). Taken together with existing literature, this study suggests that the patterns of migration of Atlantic salmon post-smolts through the inshore marine coastal zone are likely highly environment specific.

Life stage‐specific marine migration and spatial behaviour of sea trout (Salmo trutta) from two coastal rivers

J. Barry, R. J. Kennedy, C. Colfer, R. Rosell, W. Roche — Mon, 06 Apr 2026 08:39:22 -0700

Abstract

The current study utilised data from acoustic telemetry to assess movement traits important for the conservation of sea trout (Salmo trutta), providing an evidence base for future management of the species in the marine environment. The inclusion of sea trout (Salmo trutta) in Annex III of the EU Nature Restoration Law (Regulation [EU] 2024/1991) marks a significant step in recognising the species' ecological importance and the urgent need to understand its marine space use. In total, 255 sea trout (n = 170 post-smolts, n = 54 finnock) from two coastal rivers were monitored between April 2018 and September 2021, with a high level of migration being observed between both natal and non-natal estuaries and open coast zones. The key findings highlight clear differences in dispersal, residency and space use both within and between post-smolts and finnock (sea trout in their first year after smolt migration). Post-smolts exhibited greater dispersal distances and longer residency in the marine array, while finnock displayed strong seasonal trends, particularly in open coastal areas, suggesting waterbody type-specific movement behaviours. On average, post-smolts dispersed farther than finnock, but average dispersal for all tagged fish was approximately 20 km from the natal estuary, confirming localised marine space use. The average duration spent at sea was 83 days for post-smolts that returned to their natal river in the same year. Tagged sea trout travelled cumulative distances of up to 276 km within the marine array during the study period. The results demonstrates that sea trout marine movement has a seasonal element, with natal estuaries acting as a key transitional zone before broader marine dispersal and highlights the importance of non-natal estuaries during summer months. The mixing of sea trout from multiple rivers in shared marine areas (e.g. estuary & inshore coastal zones) highlights the need for management at a regional scale rather than a single river approach. The marine movement traits presented here provide essential insights to support policymakers and managers to make informed decisions that promote sustainability of sea trout populations.

Correction to ‘Spatio‐temporal assessment of nearshore fish communities in a temperate estuary using functional and community metrics for restoration and management’

Mon, 06 Apr 2026 00:40:09 -0700

Journal of Fish Biology, EarlyView.

Intestinal characteristics and microbial community composition of rapid‐growing golden‐backed carp (Cyprinus carpio var. Jinbei) in rice fields

Wed, 01 Apr 2026 06:35:39 -0700

Abstract

The golden-backed carp (Cyprinus carpio var. Jinbei) is a fish species that thrives in rice fields. Some populations of this species are known to demonstrate rapid growth; however, the underlying mechanisms and characteristics of rapidly growing groups remain unclear. To investigate these mechanisms, offspring from a single pair of golden-backed carp parents, which were of similar initial body size and morphological specifications, were stocked in a rice field and reared for 93 days. Histological, enzymatic and high-throughput sequencing methods were used to compare differences in intestinal histological morphology, digestive enzyme activity and intestinal microbial communities among different growth groups. Histomorphologically, villus height and the villus-height-to-crypt-depth ratio significantly differed among the three growth groups, whereas villus width, crypt depth, muscle layer thickness and goblet cell abundance did not vary. Amylase and trypsin levels in the rapid-growth group were significantly higher than those in the moderate- and slow-growth groups. The gut microbiota in the rapid-growth group was characterized by the presence of the phyla Firmicutes (41.40%), Proteobacteria (35.33%), Clostridia (16.21%) and Actinobacteria (3.52%). At the genus level, the dominant taxa included Streptococcus (31.22%), Bartonella (29.45%) and Cetobacter (16.21%). In rice fields, golden-backed carp with different growth rates exhibit different survival strategies. The adjustment of survival strategies results from the combined effects of digestive tract morphology, key digestive enzyme activity and specific intestinal microbial communities. This study further demonstrates the adaptability of golden-backed carp to paddy-field culture, providing a reference for improving the efficiency of ecological farming and breeding systems in paddy fields.

Reproductive biology of the starry grouper, Epinephelus labriformis (Perciformes: Serranidae): Gonadal development, sex change and sexual pattern

Wed, 01 Apr 2026 06:25:16 -0700

Abstract

The reproductive biology of the starry grouper, Epinephelus labriformis, in Mazatlan Bay, Mexico, was studied through histological analysis of the gonads. A total of 527 fish were examined through weekly sampling from March 2017 to March 2018. In this species, the gonads are bilobed and connected to a common gonoduct. E. labriformis exhibits monandric protogynous hermaphroditism, with a female-to-male proportion of 1.5 females:1 male in fully mature animals. In females, six ovarian phases were identified, and the oogenic cycle was analysed in 314 females, classified as asynchronous. The gonadosomatic index increased from 0.13 in the immature phase to 3.35 at maturity, declining to 1.16 post-spawning. Transforming testes (n = 95) revealed four stages of sex change, during which ovarian tissue is progressively replaced by testicular tissue. Males and transforming individuals appeared in larger size classes, with no females recorded beyond 27.5 cm total length (L _t). Females reach sexual maturity at 17.2 cm L _t. In comparison, males mature at 19.42 cm L _t. Sex change occurs in individuals with total lengths ranging from 20 cm to 33.5 cm L _t, with an average size for sex change of 24.7 cm. Our findings define the reproductive strategy of E. labriformis. They also provide actionable guidelines for fisheries management in Mexico. In the absence of specific regulations in Mexico, we recommended establishing a minimum catch size between 24 and 27 cm L _t and seasonal protection during the reproductive period to preserve spawning potential and maintain a balanced sex ratio in the population.

Publication lags are barriers to conservation in South American ichthyology

Elioenai da Silva Oliveira, Felipe Polivanov Ottoni, Josie South — Wed, 01 Apr 2026 01:01:01 -0700

Journal of Fish Biology, EarlyView.

DNA‐based identification of anadromous fishes (Alosa spp., Family Clupeidae) in stomach contents of marine groundfish

Landon P. Falke, Stacy Rowe, Yuan Liu, Timothy F. Sheehan — Tue, 31 Mar 2026 05:45:48 -0700

Abstract

Using DNA techniques for prey identification is an emerging approach for enhancing the precision and accuracy of trophic information. We evaluated the effectiveness of DNA-based prey identification in conjunction with visual stomach content analysis of commercially important groundfish in the nearshore Gulf of Maine, with a focus on distinguishing consumed anadromous (Alosa spp.) and closely related marine prey (Atlantic herring Clupea harengus, Atlantic menhaden Brevoortia tyrannus). DNA barcoding of 179 consumed prey specimens provided species- or genus-level identification in 122 cases (68.2%), including 104 improvements to taxonomic resolution and three conflicting results compared to visual identifications. Combining DNA-based identifications of partially or well-digested prey with the broader visual analysis substantially improved quantification of a diet metric, frequency occurrence, as a proxy for the relative diet contributions of anadromous and marine clupeids. Body size measurements of consumed Alosa spp. identified using DNA were consistent with year-0 or year-1 juvenile life stages. Possible limitations to success rates of DNA assignment included the quality of sample preservation (ethanol), reference database quality (accuracy of voucher specimen identification) and sequencing errors (miscalling of nucleotide bases). Despite this, the integration of molecular methods substantially improved the interpretability of trophic interactions involving morphologically similar prey with ecologically important differences in life history. These results highlight how the targeted application of DNA-based prey identification can complement conventional diet analyses by improving the quantification of trophic interactions that ultimately govern ecosystem processes.

Redefinition of Stemonosudis intermedia (Ege, 1933) and description of a new species from the western Atlantic Ocean (Aulopiformes: Paralepididae)

Hsuan‐Ching Ho, Katherine E. Bemis — Mon, 30 Mar 2026 19:46:02 -0700

Abstract

We examined specimens of slender barracudina in the genus Stemonosudis collected from the western Atlantic Ocean. Investigation revealed that seven specimens represent the first adult records of Stemonosudis intermedia (Ege, 1933), previously known only from juveniles. We redescribed S. intermedia based on the holotype and newly recognized adult and juvenile specimens, and using this ontogenetic series, we document changes in coloration from light-brown juveniles to black adults. We also determined that some specimens from the western Atlantic Ocean previously identified as S. intermedia represent a new species, which we describe herein based on three adults and five juvenile specimens. The new species differs from congeners by having 43–44 anal-fin rays, 117–121 total vertebrae and a pale mouth, gill chamber and gill arches, among a combination of other characters. We also provide information on the lectotype of S. similis (Ege, 1957), which remains known only from the type series.

Contrasting population genomic structuring of northern pike (Esox lucius L.) in fresh‐ and brackish water environments: Implications for management and conservation

Alfonso Diaz‐Suarez, María‐Eugenia López, Göran Sundblad, Anti Vasemägi — Mon, 30 Mar 2026 00:00:00 -0700

Abstract

Understanding the factors that shape population genetic structure is crucial for advancing evolutionary studies and developing effective management and conservation strategies. The northern pike (Esox lucius L.) is a top teleost predator that inhabits fresh and brackish water environments in the northern hemisphere. Pike populations in the brackish Baltic Sea typically display strong genetic structuring, with coastal sympatric populations that separate during spring for spawning in either shallow, sheltered brackish bays or in freshwater tributaries and wetlands. In contrast to the Baltic Sea, genomic structuring in freshwater environments, particularly in large lacustrine systems, remains poorly understood. To address this gap, we used restriction site-associated DNA-sequencing to assess the genetic structure and diversity of northern pike in two ecologically contrasting habitats: freshwater Vänern Lake, Sweden (8932 single nucleotide polimorphisms [SNPs]), and the brackish Baltic Sea around Saaremaa, Estonia (6899 SNPs). The results show strong genetic structuring and lower genetic diversity in brackish environment compared to the higher genetic diversity and extremely low genetic structuring observed in freshwater habitat. We found no evidence of divergent selection within environments. However, we identified 187 outlier SNPs and 62 outlier genes distinguishing the brackish and freshwater environments, potentially reflecting adaptation to salinity. Notably, several of these genes are associated with key biological processes, including osmotic stress regulation (akap13), early development (tfap2a) and pathogens response (tlr18). From a fisheries management perspective, our results indicate that the freshwater system can be managed as a single stock, while strong population structuring among Baltic coastal pike likely requires either large-scale solutions and/or population-specific fine-scale management efforts to maintain the genetic and life-history diversity among brackish coastal pike populations.

Sexual selection and reproductive success in mesocosm populations of African annual killifish

Jakub Žák, Klára Mrkvová, Martin Reichard — Sun, 29 Mar 2026 18:51:21 -0700

Abstract

Variation in individuals’ ability to obtain mates generates sexual selection, which typically acts more strongly on males and can produce pronounced differences in phenotypes between the sexes (i.e., sexual dimorphism). The dynamic of sexual selection and individual reproductive success is considerably affected by the availability of reproductive territories. Nothobranchius furzeri Jubb, 1971 (a model system in aging studies) inhabits temporally and spatially constrained ephemeral savanna pools where it lays its eggs in the muddy substrate. Males of the species are large and aggressive; nonetheless, it is unclear why it is dimorphic, whether they form territories and how females select their partners for mating. We released 96 individuals into 12 semi-natural mesocosms with either a clustered or a dispersed configuration of spawning substrate. We found that males formed body size-dependent dominance hierarchies. Dominant males were territorial and nearly monopolized matings when the substrate was defendable. Females engaged in 40% more spawning acts within a spawning bout with dominant males. Therefore, the intersexual size dimorphism appears to be maintained by the higher competitive ability and reproductive success of large males. Females were less aggressive, but were harassed by males, and fed three times more than males. Overall, we demonstrated under a semi-natural setting that the mating system in N. furzeri is dominated by large males, which become territorial when the spawning substrate is limited (clustered), a likely situation in the environment of ephemeral pools.

Distributional patterns and habitat associations of sturgeon chub in western Missouri River tributaries of South Dakota

Mitchell R. Magruder, Jenna P. Ruoss, Mark A. Pegg — Sun, 29 Mar 2026 17:51:05 -0700

Abstract

There is a growing body of literature that suggests riverine fish are some of the most threatened taxa on a global scale. Similarly, the literature suggests less-altered tributaries may offer refugia for large-river specialists. The greater Mississippi River basin, including the Missouri River system, has been subjected to anthropogenic changes in flow, habitat fragmentation and turbidity, leading to declines in multiple native fish species. Small-bodied fish species are exceptionally susceptible to changes in habitat, resulting in a heightened risk of extinction. The sturgeon chub Macrhybopsis gelida belongs to the family Leucisidae and is a benthic, small-bodied minnow native to the greater Mississippi River basin and is highly adapted for life in large, turbid and free-flowing rivers. Sturgeon chub distribution, habitat use and associations with other species are well studied in large mainstem rivers, but remain poorly understood in tributaries, which may serve as refugia as mainstem populations decline. Evidence of recent declines in the upper Missouri River highlights the need to better understand the role of these tributary systems. We therefore assessed the distribution and abundance of sturgeon chub populations in western Missouri River tributaries of South Dakota, evaluated broad-scale abiotic and biotic influences on their distributional patterns and characterized their habitat associations. Sturgeon chub were captured in the Cheyenne (n = 81), White (n = 331) and Little White (n = 71) rivers but were absent from the Little Missouri and Grand rivers. Sturgeon chub distributions were limited to lower areas of all rivers (i.e. closer proximity to mouths) where stream width, turbidity, discharge and observed habitat complexity (i.e. greater diversity of mesohabitats present) were highest. Furthermore, sturgeon chub were often found in association with high abundances (≥10% of catch) of flathead chub Platygobio gracilis and Hybognathus spp. (plains minnow Hybognathus placitus and western silvery minnow Hybognathus argyritis). Sturgeon chub generally used main- or secondary-flowing macrohabitats and were predominantly found in channel border or thalweg mesohabitats in most sampled reaches. Mesohabitats with greater bottom velocities [mean = 0.34 m/s, standard deviation (SD) = 0.11] and higher percentages of gravel (mean = 44, SD = 24) in the substrate were more likely to contain sturgeon chub in the White and Little White rivers, whereas greater depths (mean = 0.49 m, SD = 0.19) were associated with their presence in the Cheyenne River. Our study highlights the importance of tributaries as a surrogate to the mainstem Missouri River regarding sturgeon chub persistence that may be applicable to other imperilled fish species.

Diet of juvenile skipjack herring Alosa chrysochloris: Ontogenetic shifts, predator–prey size ratios and mouth gape allometry

Sat, 28 Mar 2026 08:56:35 -0700

Abstract

The skipjack herring Alosa chrysochloris inhabits Gulf of Mexico drainages, primarily the Mississippi River Basin, and estuarine environments in the Gulf of Mexico. The trophic ecology of the skipjack herring is poorly understood, therefore we quantified the length, mouth gape and gut contents of juvenile skipjack herring from the Mississippi River (fish n = 6), Illinois River (fish n = 181) and Ohio River (fish n = 255) and tested for changes in diets and predator–prey size ratios during ontogeny. We identified statistically significant changes in prey type consumption during ontogeny. Aquatic insects dominated the diets of skipjack herring <40 mm standard length (SL), with zooplankton and terrestrial insects also contributing to diets. The diets of skipjack herring >40 mm SL were primarily composed of fishes. The most prevalent fish species consumed by skipjack herring were invasive bigheaded carps Hypophthalmichthys spp. and preliminary evidence indicated that inter-annual variation in the consumption of bigheaded carps was driven by variation in juvenile bigheaded carp abundance. Additional research is needed to determine if the enhancement of native skipjack herring populations could be used as a tool to limit bigheaded carp population sizes. Skipjack herring SL and mouth gape were both significantly positively correlated with maximum, median and minimum sizes of prey consumed. There were allometric changes in the mouth gape of juvenile skipjack herring, with the ratio of mouth gape to SL increasing until ~80 mm SL, then gradually declining. Maximum mouth gape to SL ratios corresponded to substantial increases in the consumption of fishes, indicating that mouth gape allometry may facilitate the ontogenetic transition to piscivory in the skipjack herring. This study improves our understanding of skipjack herring ecology and provides data that can be incorporated into future ecological and evolutionary research, such as the development of food web models.

The state of knowledge on four families of Syngnathoidei fishes (Teleostei: Syngnathiformes): Aulostomidae, Centriscidae, Fistulariidae and Solenostomidae

Syd J. Ascione, Elsa Camins, Miguel Correia, Amanda C. J. Vincent — Sat, 28 Mar 2026 08:46:00 -0700

Abstract

Knowledge on the ecology and life-history traits of coastal marine species is vital to inform their conservation and management, especially as their coastal habitats come under increasing threats. However, such data have never been collated for four of the five families in the suborder Syngnathoidei—the close relatives of the better-studied Syngnathidae (seahorses, pipefish and seadragons). Here, we present the first review of the state of knowledge on four families in the suborder Syngnathoidei: Aulostomidae (trumpetfish), Centriscidae (bellowsfish, snipefish and razorfish), Fistulariidae (cornetfish) and Solenostomidae (ghost pipefish). We analysed literature from a variety of repositories (n = 761 sources) and extracted information on these fishes' ecology, life-history traits, population parameters, uses and pressures. The families with the widest breadth of available information were Fistulariidae and Aulostomidae, whereas Centriscidae and Solenostomidae exhibited major data gaps across nearly all data fields. Across all families, morphologies, global ranges and maximum lengths are relatively well documented, whereas data concerning survival, reproduction and population metrics are extremely limited. This review uncovered information for all species which, to date, have not been considered in their International Union for Conservation of Nature (IUCN) Red List assessments, and highlighted data gaps which impede conservation planning. Our gap analysis provides an important call-to-action, establishing key research priorities to fill gaps in our understanding, to better inform future conservation assessments and management efforts for these distinctive but understudied fishes.

Distribution and ecology of the four Macrourus species by‐caught in the longline fishery at South Georgia, Southern Ocean

Sat, 28 Mar 2026 08:35:44 -0700

Abstract

Although Macrourus species are the main by-catch across Southern Ocean longline fisheries, including around South Georgia, the lack of species-specific data has hindered effective management and ecological understanding. Aggregation of macrourids at genus level masks critical interspecific differences in life-history strategies and vulnerabilities to fishing. Here, we provide the first comprehensive biological assessment of the four macrourid species caught in South Georgia waters: Macrourus caml, Macrourus carinatus, Macrourus holotrachys and Macrourus whitsoni. Using fishery and observer data collected in 2018–2022, we reveal pronounced female-biased sex ratios in three species (M. holotrachys, M. carinatus and M. caml), strong depth-based segregation by body length, distinct distributions and habitat preferences related to environmental features (bathymetric depth and slope, primary productivity and temperature). By-catch rates were highest in the southern region of South Georgia and varied across species: M. holotrachys was the most frequently caught and had a wide spatial and bathymetric distribution (∼1000–1750 m); M. caml was the second most caught and appeared the most flexible in terms of habitat use; M. carinatus was mainly caught in the west, including at Shag Rocks; and M. whitsoni was caught less frequently and in deeper water (> 1500 m), mostly in the northeast and east, and had the most restricted distribution. These interspecific differences underscore the need for species-level assessments of fisheries risk and improved data collection to fill knowledge gaps. Overall, this study provides a critical foundation for understanding the ecology of Macrourus species in sub-Antarctic ecosystems and highlights that additional data are required for by-caught species to aid species-level management in toothfish longline fisheries in the CCAMLR area.

Transcriptomic evidence suggesting a Trojan horse‐like synergistic effect in exposures to nanoplastics and benzo[a]pyrene on a yellowfin sea bream muscle derived cell line

Fri, 27 Mar 2026 23:28:52 -0700

Abstract

In this study, a new cell line named yellowfin sea bream muscle (YSBM) was successfully established by using muscle tissue from yellowfin seabream, Acanthopagrus latus, a widespread saline fish cultivated in China. The YSBM cell line was subcultured more than 100 passages and appeared to be suitable for researching gene functions in vitro, as it was able to be transfected successfully with pEGFP-N3 plasmid. Additionally, YSBM cells were found to be susceptible to red-spotted grouper nervous necrosis virus (RGNNV), suggesting that this cell line can be a valuable resource for fish virology research. Further, YSBM cells were employed in environmental pollutant exposure experiments to investigate the mechanisms of damage caused by these pollutants to muscle tissue of aquatic organisms. We exposed YSBM cells to nanoplastics (NPs), benzo[a]pyrene (BaP) and a mixture of both, and performed transcriptome analysis on the samples. Our transcriptome analyses revealed discernible variations in the effects on the cells between the groups where BaP and NPs were processed separately. Interestingly, joint treatment with the two pollutants resulted in a synergistic toxicity, an effect reminiscent of the hypothesized ‘Trojan horse’ mechanism, where the mixture of BaP and NPs demonstrated mutually augmenting toxicities on aquatic organisms. Overall, our results suggest that the YSBM cell line could be a valuable tool in aquatic environmental pollution toxicological analysis. It is particularly useful for evaluating the effects of environmental pollutants on fish and their potential impact on humans via the food chain. A graphical abstract is provided to illustrate the methodology and key findings of this study. Thus, our study sheds new light on the potential risks of environmental contaminants and illustrates the usefulness of YSBM cells for environmental toxicology research.

Diets of sculpins (Myoxocephalus spp.) and Arctic char (Salvelinus alpinus) during a spring resource pulse in the Canadian Arctic

Fri, 27 Mar 2026 22:14:45 -0700

Abstract

The Arctic is one of the fastest-warming marine regions in the world, which is changing the timing of seasonal sea-ice dynamics. The annual summer breakup of sea-ice coincides with resource pulses, which provide critical food sources for consumers to exploit. Marine organisms respond behaviourally to exploit these resources, with some migrating to presumably maximize feeding opportunities, whereas others remain resident, providing an ideal model to assess potential variability in fish movements and feeding. To assess variability in how migratory and resident fishes exploit increases in resource availability associated with ice-off, we collected stomach contents from anadromous Arctic char (Salvelinus alpinus; n = 91) and resident sculpins (Myoxocephalus spp.; n = 190) in Tremblay Sound, Nunavut, Canada, during the ice-free seasons of 2017–2019. Despite eating larger prey, Arctic char experienced lower relative consumption [mean ± standard deviation (SD); 1.92% body mass ± 1.38%] than sculpins (2.88% ± 2.93%). Arctic char also had fewer empty stomachs (n = 1; 1.96%) than sculpins (n = 11; 14.7%). Of identified prey categories, 52.6% (n = 10 categories) were shared by both consumers, but notable exceptions occurred. Non-metric multidimensional scaling (NMDS) ordination revealed dietary distinctions primarily driven by Arctic char's higher consumption of fishes and copepods, whereas sculpins fed heavily on amphipods. Our findings are consistent with sedentary and benthic-oriented resident sculpins intermittently consuming small, benthic prey at high levels, whereas mobile, semipelagic, migratory Arctic char consume pelagic prey at consistent levels that likely do not impede aerobic activity. Ultimately, diets are reflective of consumer physiology but are also influenced by migratory versus resident movement strategies and likely interannual variation in prey abundance, providing insight into strategies used by fishes in the extremely seasonal Arctic, which may become increasingly consequential with climate change.

Isolated in the highlands, found in the museum: A new species of Characidium (Crenuchidae) from a Bolivian National Park, with a CT scan revealing features

Leonardo Oliveira‐Silva, Karina Or, Angela Zanata, Scott A. Schaefer — Fri, 27 Mar 2026 00:52:06 -0700

Abstract

A new species of Characidium is described from a small, isolated river in the highland areas of Noel Kempff Mercado National Park, Bolivia. The new taxon can be diagnosed by the presence of a relatively broad and conspicuous dark midlateral stripe extending from the tip of snout to the base of the caudal fin, markedly darker than the vertical bars (when present), added to the absence of a distinct humeral blotch. Additional distinguishing features include a complete lateral line, presence of adipose fin, 12 circumpeduncular scale rows, four horizontal scale rows above the lateral line, presence of the parietal branch of the supraorbital canal and a conspicuous basicaudal spot. Some specimens also exhibit reddish-brown pigmentation on the paired, dorsal and caudal fins, a condition otherwise restricted to few congeners. This discovery highlights the hidden fish diversity of poorly explored highland rivers and protected areas within Neotropical region. In addition, we discuss osteological features of the Weberian apparatus, documented for the first time in the genus using computed tomography (CT) scan imagery. Also, geomorphological processes that may have influenced the isolation of the new species on the Huanchaca Meseta are discussed.

First genetic confirmation of the smooth hammerhead shark (Sphyrna zygaena, Linnaeus, 1758) in French Polynesian waters

Wed, 25 Mar 2026 07:59:20 -0700

Abstract

The smooth hammerhead shark (Sphyrna zygaena) has never been formally confirmed in French Polynesian waters. Observations of solitary hammerhead sharks suggested the presence of an unrecorded species. Two specimens captured off Tahiti were morphologically and genetically examined. Both matched traits of the smooth hammerhead and COI barcoding confirmed >99% similarity to reference sequences in the NCBI and BOLD databases. This record extends the known range of S. zygaena to the central South Pacific and highlights the role of citizen observations in detecting rare oceanic sharks, which is important to regional conservation frameworks.

Calcium and magnesium ions are the main intrinsic factors that induce the activation of stickiness in the eggs of the fat greenling (Hexagrammos otakii)

Zhuang Xue, Yuqing Yan, Chenghao Qiu, Juan Chang, Wei Wang, Hongyu Pu — Wed, 25 Mar 2026 07:36:33 -0700

Abstract

In fish artificial breeding, adhesive eggs present a significant challenge for fertilization and reduce hatching success rates. Understanding the specific factors and mechanisms that influence egg adhesiveness, as well as developing effective de-adhesion methods, is crucial for improving fish reproduction efficiency. Fat greenling (Hexagrammos otakii), a typical marine teleost species that produces adhesive eggs, is widely distributed in the northwest Pacific Ocean and is considered a promising candidate for aquaculture. In this study, H. otakii eggs were used as a model to qualitatively analyse the effects of different pH levels (6.0, 7.0, 8.0 and 9.0), osmotic pressures (100, 400 and 1000 mOsm kg⁻¹) and metal ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Mn²⁺ and Cu²⁺) on egg adhesiveness. In addition, scanning electron microscopy was employed to examine the ultrastructural changes on the egg surface under different conditions. The results indicated that Ca²⁺ and Mg²⁺ are the primary factors in seawater that induce egg adhesiveness in H. otakii, while changes in pH and osmotic pressure neither triggered adhesiveness nor altered the underlying adhesive mechanism. Furthermore, the study evaluated the effectiveness of protease treatment for chemical de-adhesion. The results showed that treating the eggs with a 10 mg/L protease solution for 2 min successfully removed their adhesiveness, confirming the feasibility of chemical de-adhesion. This research provides significant theoretical insights for optimizing the artificial breeding techniques of H. otakii.

Time‐calibrated relationships of a rare cave catfish (Trichomycterus rubbioli): Shedding light on troglobitic lifestyle origin in the Brazilian caatinga

Wed, 25 Mar 2026 01:40:52 -0700

Abstract

Catfishes of the subfamily Trichomycterinae comprise the most diverse fish group with species adapted to live in Neotropical caves, but past evolutionary scenarios that have driven the origin of these troglobitic species remain unknown. We herein investigate the phylogenetic position of the cave-restricted Trichomycterus rubbioli, endemic to the semi-arid Caatinga of northeastern Brazil, through a time-calibrated molecular phylogenetic analysis of a broad sample of trichomycterine taxa (84 spp), using two nuclear and two mitochondrial genes (3030 bp). The analysis supported T. rubbioli as a member of the Trichomycterus s.s. clade endemic to eastern South America and an early Miocene origin for the T. rubbioli lineage. The combination of available data suggests that the T. rubbioli lineage adapted to the troglobitic lifestyle between the Middle and Late Miocene, a period when the semi-arid conditions of the Caatinga biome became established and consequently streams of the region became seasonal. This past scenario would be responsible for extinction of epigean trichomycterines while preserving the lineage within the cave system. Morphological characters of the troglobitic ‘Trichomycterus’ itacarambiensis from the transition area between the Cerrado and the Caatinga indicate distant relationships with T. rubbioli, suggesting an independent evolutionary event of cave colonization.

Changes in size‐at‐age of juvenile Atlantic salmon cohorts over the past 50 years and linkages to environmental factors

Wed, 25 Mar 2026 00:00:00 -0700

Abstract

Quantifying the potential effects of climate change on juvenile salmonid body length at a large spatiotemporal scale is challenging given the multitude of biological processes and methodological constraints. In the present work, we analysed potential changes in size-at-age of juvenile Atlantic salmon cohorts over the past 50 years in the Miramichi and Restigouche rivers (Canada), and how they relate to environmental factors. To do so, we built a novel age-structured hierarchical model expanding on the von Bertalanffy growth function (VBGF) framework to incorporate environmental parameters and the cessation of growth in winter independently among age classes. This model supports the prediction that size at the end of the growing season of all life stages increased from 1970 to 2021 in the Restigouche River and decreased (marginally) over the same period in the Miramichi River. This difference may be due to the Miramichi River being warmer and less suitable for growth than the Restigouche River. However, the inclusion of temperature metrics, density and discharge to growth parameter K did not improve the VBGF models. Similarly, size at the end of the growing season was related negatively to fish density, but no clear relation with temperature metrics or discharge was identified, despite important differences in temperature regimes among rivers. Thus, although trends in size at the end of the growing season followed our predictions given global warming, linking them explicitly to the expected growth–temperature relationship was challenging given the spatial and temporal scales of the data, and perhaps due to the influence of alternative factors.

Male‐territory‐visiting polygamy in the sand‐dwelling goby Fusigobius inframaculatus (Gobiidae) inhabiting reef caves

Ryoga Seiwa, Yoichi Sakai — Tue, 24 Mar 2026 04:16:37 -0700

Abstract

We conducted an observational field survey of the innerspotted sandgoby Fusigobius inframaculatus on reefs of Kuchierabu-jima Island, southern Japan, to investigate its mating system. Individuals of the goby maintained home ranges on sandy bottoms within rocky caves or beneath overhangs that served as shelters. Of 34 identified individuals, 32% disappeared during the 4-month reproductive season, and nearly all had disappeared by the next reproductive season, indicating a high mortality rate. Territorial males constructed spawning nests on the ceilings of these cavities and mated with multiple females. The mating groups were isolated from one another and intergroup movements were rare, suggesting restricted movement under a strong predation pressure. Although facultative harem polygyny was observed in some local groups, most females visited male territories from outside for spawning and often changed mates. Based on the segregated spatial relationships of home ranges between sexes and unstable mating relationships, the mating system was characterized as male-territory-visiting polygamy. The goby exhibited sexual dimorphism in body size, with males being the largest individuals within local groups, and exhibited subtle and transient coloration changes in males during courtship, which may function as female choice traits. Our results suggest that the polygamous mating system in F. inframaculatus is maintained even under constraints of mate availability due to limited mobility within the narrow sheltering habitat at the boundary between sandy bottoms and rocky substrates.

Two‐dimensional otolith size trends in myctophid fishes

Víctor M. Tuset, M. Pilar Olivar, Amalia Manjabacas, Antoni Lombarte — Tue, 24 Mar 2026 04:05:09 -0700

Abstract

Lanternfishes are a key food source for marine and terrestrial predators, and play an important role in energy transfer between surface waters and deeper layers. This study investigates otolith size variation in 105 myctophid species included in the AFORO database. The study covers the five Myctophidae subfamilies: Diaphinae, Gymnoscopelinae, Lampanyctinae, Myctophinae and Notolychninae. Several measurements were taken from the otoliths, and relative shape and sizes indices were calculated for the different fishes. Morphometric analyses revealed that Diaphinae and Gymnoscopelinae possess the largest otoliths in terms of length and width, whereas Notolychninae exhibited the smallest. Gymnoscopelinae were further characterized by more elliptic otolith shapes, while Diaphinae displayed proportionally larger otoliths relative to fish size. Non-linear regression between otolith length and fish length was performed for 59 species, providing complementary data for understanding prey–predator relationships. Also, loess regression between the otolith relative size and fish size showed different growth patterns among species, which could suggest dissimilar metabolic activity. Our study provides a tool that will improve future food webs and ecological studies on otolith size in other fish taxa.

Range extension and first records of Coryphaenoides striaturus Barnard, 1925 and Coryphaenoides subserrulatus Makushok, 1976 (Macrouridae: Gadiformes) in Brazilian waters, Southwest Atlantic, using integrative taxonomy

Fri, 20 Mar 2026 21:49:45 -0700

Abstract

Coryphaenoides Gunnerus, 1765 comprises 66 valid species of deep-sea fishes commonly known as grenadiers, with 6 previously reported from Brazilian waters. Here, we make the first records for Coryphaenoides striaturus and Coryphaenoides subserrulatus on the Brazilian continental slope. Both species are distributed in the subtropical regions of the Southern Hemisphere, and the former is being reported for the first time in the Southwest Atlantic, and the latter has its distribution range extended northward. The identifications were confirmed by a unique combination of morphological characters and DNA barcoding using the cytochrome oxidase subunit 1 (COI) gene.

The emergence of pathogens on fish in an impacted estuary and the role of non‐native piranhas in a potential bacterial infectious outbreak

Fri, 20 Mar 2026 21:19:36 -0700

Abstract

As many tropical aquatic ecosystems worldwide, the Doce River estuary (DRE, southeastern Brazil) has increasingly faced multiple anthropogenic threats, including deforestation, mining, species introduction and water management. The 2015 collapse of the Fundão iron ore tailings dam severely changed water properties and increased heavy metal concentration in sediment. However, the potential synergistic effects of the observed threats on fish populations remain largely unknown. After detecting an elevated number of fin lesions in DRE fishes, we used the catfish Genidens genidens (Cuvier, 1829) to investigate whether such mutilations originated from fin-nipping by non-native piranha or emerged as a result of fin rot disease through bacterial infection. One third of the examined individuals had fin lesions in the DRE, whereas no conspecific exhibited such lesions in two control estuaries where piranhas are absent; lesions were restricted to the caudal fin, a region known to be targeted by fin-nipping piranhas. Independently of the presence of fin lesion, culture of fins and livers indicated higher prevalence and variety of bacterial strains in DRE individuals than in a control area. Piranhas likely contribute to the fin lesions in DRE fishes. However, the higher prevalence and variety of bacterial pathogens as well as of liver and kidney disorders identified in fin-healthy and mutilated fishes of the DRE suggest that the heavily metal-polluted conditions in the DRE may be associated with the emergence of bacterial infections in fish.

Points vs. passes: A comparison between electric fishing techniques for sampling fish populations in upland headwater streams

Reagan H. Pearce, Martin R. Perrow, Mark L. Tomlinson, Kirsty A. Turner — Fri, 20 Mar 2026 20:55:59 -0700

Abstract

Point-abundance sampling by electric fishing (PASE) was compared with single-pass (DF1) and triple-pass depletion sampling (DF3) electric fishing on the same reaches of four headwater streams sampled over multiple years in the Ribble catchment, UK. Juvenile salmonids, mostly brown trout Salmo trutta with some Atlantic salmon S. salar, or the sculpin, common bullhead Cottus perifretum, dominated the species-poor fish assemblage in all streams. Generalised linear mixed models and linear mixed models comparing differences in numerical (ind. m⁻²) and biomass density (g m⁻²) found that PASE generally returned statistically significant higher estimates for both measures compared to DF1, with the exception of C. perifretum. In comparison to DF3, PASE tended to underestimate the numerical density of the different species and groups, but the difference was not significant for S. trutta, the dominant salmonid. Moreover, biomass density estimates for all fish combined, combined salmonids and S. trutta were not significantly different. Any differences between PASE and DF3, including for Simpson's Diversity Index and fish median length, were mostly linked to C. perifretum, a small, benthic and cryptic species with low capture probability. Overall, for free-swimming, commercially important salmonids, PASE performed comparably with DF3 and outperformed DF1. This study suggests that PASE is generally preferable to DF1 and may be a useful alternative to DF3 with the advantages of rapid deployment through reduced sampling effort alongside minimal disturbance and lessened concern over fish welfare. Further comparison of PASE with DF and more research to better verify the effective sampling area of PASE is warranted.

Ichthyofaunal diversity of the Canje River (Guyana): A distinctive lowland fauna between the Berbice and Corentyne Rivers, supported by a DNA barcode repository

Fri, 20 Mar 2026 05:55:15 -0700

Abstract

Guyana, and the Guianas more generally, exhibit some of the highest examples of biodiversity and regional endemism in the Neotropics. However, much of this diversity is still unknown, with the first modern list of freshwater fishes from Guyana compiled only in 2022. We continue to build on prior efforts in Guyana and provide an annotated list of fishes collected from the Canje River, a lowland tributary of the Berbice River. The Canje is also adjacent to the Corentyne River, raising the question of whether the Canje's fauna more closely resembles the Berbice or the Corentyne. A total of 92 sites were sampled in the Canje River during both high and low water seasons in 2023, 2024, and 2025. These expeditions yielded 87 species from 63 genera representing 28 families and seven orders. Characiformes dominated collections in terms of species. In addition to collecting several taxa once thought to be endemic only to the upper Berbice River, we report the first record of Sternopygus sabaji in Guyana, as well as several likely undescribed taxa. Contrary to expectations, the Canje was not particularly similar in faunal overlap to either the Berbice or the Corentyne, providing an example of high endemicity and beta diversity in neotropical lowland rivers.

First record of young‐of‐the‐year smooth hammerhead (Sphyrna zygaena) in coastal waters of Galicia, northwest Spain

Xabier Pin, Kenn Papadopoulo, Pablo Covelo, Gonzalo Mucientes — Fri, 20 Mar 2026 05:44:05 -0700

Abstract

The smooth hammerhead (Sphyrna zygaena) is typically considered an oceanic species and is only rarely observed in the cooler coastal waters of the northeastern Atlantic. On 20 December 2024, a juvenile S. zyganea was captured at 25 m depth in the inner Ría de Pontevedra (Rías Baixas, northwest Spain). This represents the first verified record of a young-of-the-year individual in Galicia, and potentially across the entire Iberian Peninsula. This observation, together with four confirmed adult sightings in Galician waters in recent years, indicates the sporadic presence of the species far beyond its recognised nursery and distributional range. Such occurrences may reflect an emerging northward or inshore shift, potentially linked to climate-driven changes in regional oceanographic conditions. Documenting these atypical events enhances our understanding of hammerhead shark ecology in temperate Atlantic systems and underscores the need to identify potential nursery habitats within European waters.

Skipped spawning in a protandric hermaphrodite: Elucidating the physiological mechanisms in common snook Centropomus undecimalis using reproductive biology and energetics

Fri, 20 Mar 2026 05:34:02 -0700

Abstract

Recent acoustic telemetry research has demonstrated that a portion of the common snook Centropomus undecimalis population in Florida skips annual spawning; however, the details of why some individuals skip spawning are unclear. We conducted a comprehensive study of C. undecimalis reproductive biology to determine if a certain population demographic (e.g. size, age, sex, biological condition) skips spawning in a representative estuary in Florida (Tampa Bay). Reproductive parameters, specifically histological examination of ovaries and testes, analysis of reproductive hormone levels and estimates of energetics including fish condition, hepatosomatic and mesenteric fat indices, were analysed for 254 females and 210 males over two consecutive spawning seasons (2016 and 2017). The results agreed with the known reproductive biology of the species and provided a more comprehensive description of developmental patterns throughout the spawning season. Fish that skipped spawning, defined here as an individual of reproductively mature size having both undeveloped gonads and undetectable levels of primary hormone (17β-estradiol in females, 11-ketotestosterone in males), represented 18% of fish sampled. Skip spawning individuals were collected from both estuarine and riverine sites, and were predominately smaller and younger females that had spawned at least once previously as females. Fish that skipped spawning had a lower body condition, a lower fat index and, in particular, a lower liver index. As skipped spawning was predominately observed in younger and smaller female C. undecimalis that were energetically depleted, we suggest that the combination of sex transition from male to female, followed by participation in spawning in the next season, leads to most instances of skipped spawning for the species.

Reproductive plasticity and environmental tolerance of invasive African catfish (Clarias gariepinus) in a tropical Brazilian river

Michelle Torres Dumith, Alejandra Filippo Gonzalez Neves dos Santos — Thu, 19 Mar 2026 02:59:10 -0700

Abstract

Invasive alien species (IAS) pose a significant threat to biodiversity, particularly when endowed with high ecological and reproductive plasticity. The African catfish, Clarias gariepinus, is one such species, widely recognized for its ability to colonize and establish in diverse tropical ecosystems. This study evaluated the reproductive success of C. gariepinus in a tropical environment by examining gonadal maturation stages, reproductive indices and water physicochemical variables associated with reproduction. The analysis revealed a population predominantly composed of adult individuals at various reproductive stages, with a higher concentration upstream during the dry season. The species exhibited continuous reproduction throughout the year, irrespective of body size, demonstrating both high fecundity and notable environmental flexibility. Dobriyal's Reproductivity Index (DI) proved effective in identifying gonadal maturation patterns independently of somatic size and is particularly useful under conditions of limited sampling. Statistical analyses revealed a strong association between DI and key physicochemical parameters (i.e., particularly elevated dissolved oxygen concentrations and pH values within optimal ranges) which collectively influence species distribution and reproductive success. These findings underscore reproductive plasticity and environmental tolerance as pivotal strategies underpinning the invasive potential of African catfish in tropical systems. We conclude that ongoing monitoring and targeted management interventions are crucial for mitigating the ecological impacts of C. gariepinus and alleviating pressure on native fish communities.

Evidence of a marine larval stage in coastrange sculpin Cottus aleuticus from a small coastal stream in California, USA, based on otolith strontium isotopes

David E. Rundio, Rachel C. Johnson, Christopher J. Donohoe — Thu, 19 Mar 2026 02:46:20 -0700

Abstract

Cottus aleuticus (coastrange sculpin) is one of two North American facultatively amphidromous sculpins, but habitat use during its planktonic larval stage is poorly documented. We analysed strontium isotopes (⁸⁸Sr and ⁸⁷Sr/⁸⁶Sr) in otoliths of 10 adult C. aleuticus from a small coastal California stream. All showed elevated ⁸⁸Sr signal intensities in the otolith core and a marine ⁸⁷Sr/⁸⁶Sr value in the core that rapidly shifted to and then remained at the stream value. Our results confirm a marine larval stage in this species and help explain its widespread distribution across diverse watersheds.

Bony fish genomes: Status and gaps

Noelia Pérez‐Pereira, Carmen Bouza, Paulino Martínez, Diego Robledo — Wed, 18 Mar 2026 03:45:03 -0700

Abstract

Bony fish constitute an exceptionally species-rich group of aquatic vertebrates, comprising more than 95% of all living fish. The adaptive processes on the diversity of environments they inhabit make them a highly diverse group from taxonomic, morphological and evolutionary standpoints. Furthermore, among their members we find species of high economic value for global aquaculture and fisheries. This has attracted the attention of multiple research fields, from ecology or evolutionary biology to comparative genomics. However, deep biological or evolutionary studies require suitable genomic resources, particularly high-quality reference genomes, across multiple species and taxonomic groups. Here, we revise the current status of open access bony fish genome assemblies, with special emphasis on existing gaps throughout their phylogeny. Recently, there has been a boom of information and up to 1744 genomes are available, largely released in the last 5 years. They are distributed across 67 of the 72 recognized orders, where Cichliformes, Perciformes, Siluriformes, Cypriniformes and Cyprinodontiformes appear overrepresented, and across 268 families out of the 514 recognized. Overall, these figures cover around 5% of all described bony fish species. Despite five orders and 14 order-level incertae sedis families (mostly percomorphs) lacking genomic representation, high-throughput sequencing data for most gaps are available in the Sequence Read Archive repository of the National Center for Biotechnology Information. Future sequencing efforts aimed at improving assembly quality and filling the gaps in the fish phylogeny, in parallel to the evolution of sequencing and assembly technologies, will enhance our ability to answer open evolutionary questions in bony fish and provide genomic tools to boost fish production.

Occurrence of multiple congenital anomalies in Potamotrygon amandae (Elasmobranchii, Potamotrygoninae) embryos, including the first report of bicephaly

Douglas de Castro Ribeiro, Raquel Lopes Queiroz, Cristiéle da Silva Ribeiro — Wed, 18 Mar 2026 03:06:44 -0700

Abstract

Reports of teratogenic embryos in elasmobranchs have been documented in multiple species, with proposed aetiologies including environmental disturbances, genetic mutations, predation, exposure to endocrine-disrupting compounds and maternal stress. Nevertheless, complex congenital malformations such as bicephaly remain exceptionally rare, particularly among freshwater stingrays of the family Potamotrygonidae. The present study constitutes the first record of bicephaly in the genus Potamotrygon, documenting multiple congenital anomalies in two embryos from a single litter. One female embryo exhibited incomplete fusion of the anterior margin of the right pectoral fin, a malformation previously reported in batoid fishes. The second case involved a male parapagus bicephalic twin; internal examination demonstrated duplicated brains and hearts, as well as partially individualized gastrointestinal tracts, whereas the reproductive and urinary systems were shared. Skeletal assessment revealed discrete chondrocrania and precaudal vertebrae, with spinal fusion occurring at the transitional caudal region. The underlying causes of these anomalies remain unresolved. Two primary hypotheses are discussed: (1) genetic alterations, including misexpression of critical developmental regulators such as Sonic hedgehog (Shh), which has been implicated in cephalic duplication and fin malformations; and (2) maternal physiological stress, potentially linked to anthropogenic factors such as recurrent capture events, which may disrupt embryogenesis. This report broadens the spectrum of known teratological conditions in freshwater elasmobranchs and underscores the importance of further research into the mechanistic basis of congenital anomalies in this group.

Spatio‐temporal dynamics of Allis shad (Alosa alosa L.) spawning in response to environmental variability

Wed, 18 Mar 2026 02:39:56 -0700

Abstract

The Allis shad (Alosa alosa L.) is a threatened anadromous fish species whose populations have dramatically declined in recent decades due to multiple anthropogenic pressures, including habitat fragmentation, water quality degradation and overexploitation. In this study, we aimed (1) to identify the environmental and spatio-temporal drivers of spawning probability and intensity, and (2) to estimate the number of spawners over time in two major French river catchments, the Garonne and the Loire. Using generalized additive models, we found that these models performed well in predicting spawning dynamics. Spawning probability and intensity were significantly influenced by environmental variables (temperature, discharge and precipitation) and spatio-temporal factors (sampling site, river catchment, year and Julian day). Specifically, moderate increases in temperature during the pre-spawning period and low to moderate discharge on the day before or the day of spawning were associated with higher spawning probabilities and greater spawning intensity. In contrast, a temperature decrease a few days before spawning, excessively low or high discharge on the day before or the day of spawning and excessive precipitation on the spawning day were associated with lower spawning probability and intensity. Additionally, trends in the estimated number of spawners at spawning sites between 2001 and 2022 revealed a significant severe decline in both river catchments, with an average population decrease of approximately 90% in the Garonne and 75% in the Loire. These findings highlight the critical situation and the urgent need for management measures to mitigate the ongoing decline of Allis shad populations.

Histological characterisation of gonadal sex differentiation in Malabar red snapper (Lutjanus malabaricus) for aquaculture advancement

Tue, 17 Mar 2026 03:16:27 -0700

Abstract

The Malabar red snapper (Lutjanus malabaricus) is a high-value tropical marine species receiving growing attention for aquaculture development in Singapore and Southeast Asia. At present, seed production relies primarily on uncontrolled mass spawning in sea cages, a practice that lacks consistency, biosecurity and control of genetic contributions. A clear understanding of gonadal sex differentiation is essential for designing effective sex control strategies and establishing selective breeding programmes. However, the progression of gonadal development from initial differentiation through to sexual maturity in L. malabaricus remains poorly characterized. In this study, a comprehensive histological investigation of gonadal differentiation was conducted by tracking individuals from 1 to 445 days post-hatch (dph). Gonads first appeared as undifferentiated structures at 14 dph, located between the swim bladder and intestine. The onset of ovarian differentiation was observed at 77 dph, marked by ovarian cavity formation, while testicular differentiation commenced at 128 dph, indicated by the development of lobular testis structures. Oogenesis was initiated by 169 dph, marked by the first observation of oogonia, and progressed to the chromatin nucleolus oocyte stage by 249 dph. Spermatogenesis was first evident at 249 dph, based on the appearance of lobular organization and spermatogonia, and further progressed by 353 dph, when spermatocytes, spermatids and spermatozoa were observed. These observations establish the first developmental timeline of gonadal sex differentiation in L. malabaricus, identifying key morphological features that distinguish early-stage ovaries from testes. Importantly, our study also revealed a highly skewed sex ratio in a harvest-size cohort from a commercial farm, with females comprising over 85% of the population. Given the species is considered gonochoristic, this finding raises concerns about potential influences from environmental factors, hatchery practices or genetic bottlenecks, and highlights the need for further investigation under controlled conditions. Together, these findings provide essential biological benchmarks for identifying the timing of sex differentiation and suggest that the optimal windows for sex manipulation occur around 60 dph to promote testicular development and approximately 110 dph to promote ovarian development. This work lays the foundation for future sex control techniques and contributes valuable knowledge toward the development of selective breeding programmes and sustainable seed production in this emerging aquaculture species.

Brook trout populations vary in the thermal acclimation response of their myotomal muscle: Implications for the impact of climate change

Tue, 17 Mar 2026 02:52:04 -0700

Abstract

Cold-water fishes, such as salmonids, face environmental stresses resulting from climate change. We examined the thermal acclimation response of the hatchery-reared versus wild, native brook trout (Salvelinus fontinalis) to explore how the contractile properties and gene expression of their myotomal muscle might shift to mitigate the impact of a warming environment. Hatchery fish were acclimated to three temperatures (4, 10 and 20°C), while wild fish were collected across the seasons grouped by water temperature at time of collection (<6, 10–12 and >16°C). When tested at a common temperature (10°C), maximum escape swimming velocity and contractile properties such as maximum muscle shortening velocity showed a significant thermal acclimation response in both groups of fish. However, other contractile properties, such as twitch time, varied in how each population responded to the thermal environment. These fish also showed changes in the expression of a wide variety of muscle and metabolic genes with elevated temperature, providing a mechanistic foundation for differences in thermal acclimation by each population. These fish showed similar but not identical shifts in muscle function and gene expression with a warming environment, suggesting that wild populations of brook trout may vary in their thermal acclimation response across the range of this cold-water salmonid.

Intra‐annual energy density cycles of spring‐ and fall‐spawning Atlantic herring Clupea harengus reveal different reproductive allocation tactics

Joseph B. Warren, Mark J. Wuenschel, Kenneth Oliveira — Tue, 17 Mar 2026 02:43:32 -0700

Abstract

Atlantic herring Clupea harengus are total spawners that exhibit a large degree of reproductive plasticity and have substantial intra-annual variation in their energetic condition. Recent research suggests that the species may be declining in energetic condition in the northwest Atlantic Ocean from the few historical records, but comparisons in the region are complicated by the presence of spring- and fall-spawning contingents. Proximate composition analysis (water, lipid, protein and ash) results of Atlantic herring somatic tissue and gonads revealed sex-specific energy allocation patterns and generated strong predictive relationships used to estimate the energy density (ED; kJ g⁻¹ wet weight) of 1104 individuals collected between 2021 and 2023 by fishery-dependent and -independent sources. Generalized additive models showed non-linear somatic ED cycles that varied by spawning contingent and day of year. The best model included an interaction between day of year and spawning contingent, and explained 64.6% of the deviance, 12.2% more than the model without spawning contingent. Gulf of Maine and Georges Bank Atlantic herring ED was less variable in the spring compared to the fall, when there was a smaller energetic offset between contingents. Estimates of contingent-specific seasonal somatic ED cycles provide context for interpreting values across studies, evaluating long-term energetic condition trends and assessing possible environmental influences on the energy dynamics of these two spawning contingents that are managed as one stock complex.

A complex pigmentation disorder reveals energetic and ecological costs of coloration in a deep‐sea sharpnose sevengill shark

Tue, 17 Mar 2026 02:35:41 -0700

Abstract

Pigmentation is a key functional trait influencing camouflage, predator–prey interactions and energetic efficiency in marine organisms, yet its physiological and ecological consequences remain poorly understood in deep-sea sharks. Here, we describe a deep-sea shark (Heptranchias perlo) exhibiting a mosaic pigmentation disorder characterized by the coexistence of hypermelanotic, hypopigmented and amelanotic regions, indicating disruption of normal melanophore distribution and regulation. Histological examination revealed no structural or inflammatory abnormalities, supporting a non-pathological origin of the pigmentation anomaly. In contrast, condition indices indicated pronounced energetic depletion, with reduced condition factor and hepatosomatic index, while lipid extraction and Fourier-transform infrared and ultraviolet–visible spectroscopy revealed substantial depletion and altered composition of hepatic lipid reserves consistent with chronic negative energy balance relative to phenotypically normal conspecifics. We propose that disruption of countershading in hexanchiform sharks may reduce camouflage efficiency and increase energetic costs, contributing to the observed physiological compromise in sharks. Despite being based on a single individual, this integrative analysis links pigmentation anomalies to functional and energetic consequences, and underscores the need to move beyond descriptive accounts toward mechanistic assessments of coloration in marine predators, particularly in deep-sea elasmobranchs that are inherently rarely encountered.

Correction to ‘Structural and developmental insights into the muscles involved in lionfish (Pterois spp.) vocalisations’

Mon, 16 Mar 2026 20:50:32 -0700

Journal of Fish Biology, EarlyView.

Fatty acid profiles of muscle and liver reveal ontogenetic shifts in diet and reproductive investment in an undulate ray from the Bay of Biscay (northeast Atlantic)

Mon, 16 Mar 2026 03:09:47 -0700

Abstract

Elasmobranchs, with their slow growth, long lifespans and low reproductive output, are particularly sensitive to fluctuations in nutritional status and energy availability throughout ontogeny. Fatty acids serve as valuable biomarkers for studying trophic ecology, ontogenetic dietary shifts and energy allocation during key life periods such as growth and reproduction. This study examined fatty acid profiles in Raja undulata by analysing muscle and liver tissues to investigate ontogenetic dietary shifts, assess niche breadth and overlap between juveniles and adults, and explore how reproductive development influences fatty acid allocation after sexual maturity. The muscle fatty acid profiles of R. undulata varied across life stages, with adults showing a reduced trophic niche and a diet composed of higher-trophic-level prey compared to juveniles. This pattern suggested a dietary shift from a diverse, invertebrate-based diet in juveniles to more specialized predation on fish and larger crustaceans in adults. The liver fatty acid profiles varied across reproductive stages, with an increasing proportion of omega-3 (C22:6n-3, docosahexaenoic acid [DHA]; 22:5n-3, docosapentaenoic acid) and omega-6 polyunsaturated (C20:4n-6, arachidonic acid [ARA]) fatty acids, alongside a marked decline in eicosapentaenoic acid (C20:5n-3), likely reflecting its direct allocation to the ovaries. Additionally, the elevated monounsaturated fatty acids levels in adults and their decline during gametogenesis highlighted their key role as energy sources for oocyte development, supporting previous findings on reproductive energy mobilization in elasmobranchs. While DHA and ARA proportions increased, their stable absolute values suggested a different allocation pattern compared to viviparous species, potentially due to R. undulata's oviparous strategy. Our findings, in line with previous studies, showed that analysing different tissues is key to understanding how diet and energy use are linked in elasmobranchs.

A haplotype‐specific PCR strategy for rapid and cost‐effective identification of redfish species (genus Sebastes) in the North Atlantic and Arctic oceans

Valentina S. Artamonova, Aleksei Y. Rolskii, Alexander A. Makhrov — Mon, 16 Mar 2026 03:00:30 -0700

Abstract

Redfish species of the genus Sebastes are ecologically and commercially valuable components of North Atlantic and Arctic ecosystems. Accurate species identification within this group has long been controversial due to overlapping morphological traits, compounded by widespread interspecific hybridization. Methodological difficulties in distinguishing between Acadian redfish (Sebastes fasciatus) and beaked redfish (S. mentella), which occur sympatrically, have led to these species being managed as a single commercial stock in the Northwest Atlantic for decades. Additional challenges arise when differentiating catches of golden redfish (S. norvegicus) and S. mentella on the eastern Greenland slopes. Significant difficulties also occur in identifying juvenile Sebastes spp. in the Arctic Ocean. In recent years, efforts to develop genetic markers for redfish species identification have intensified. This work describes a haplotype-specific PCR assay based on mitochondrial control region (D-loop) polymorphisms for identifying North Atlantic redfish species.

The impact of isosmotic conditions on the metabolism and hypoxia tolerance of a reportedly oxyconforming teleost

Mon, 16 Mar 2026 02:40:31 -0700

Abstract

Fish must manage the competing demands of ion balance and gas exchange across the gills – a physiological tension known as the osmorespiratory compromise. In dynamic estuarine environments, the osmorespiratory compromise may be exacerbated by variable salinity and periods of hypoxia that demand high respiratory work. This study examined whether acute exposure to isosmotic conditions (9 ppt) lowers aerobic metabolism and enhances hypoxia tolerance relative to fresh water (0 ppt) in the fish Galaxias maculatus, a species that purportedly lacks oxyregulatory capacity when faced with hypoxia. Analysis via Bayesian mixed models found no impact of salinity on routine or standard oxygen uptake rates (ṀO₂). The majority of fish maintained their ṀO₂ as oxygen declined to ~10% air saturation, with only 8 of 58 individuals displaying a measurable critical oxygen saturation (O_2crit). Average O_2crit values were similar across treatments (25.3% in 0 ppt versus 24.3% in 9 ppt), though the small number of fish showing a clear threshold suggests that the average O_2crit of the species might be substantially lower. Contrary to earlier reports, our findings show that G. maculatus has an oxyregulatory capacity that aligns with other teleosts. The marked interindividual variability in ṀO₂ patterns with progressive hypoxia was a feature of this study when compared with other species, adding to a growing pattern of impressive physiological plasticity in G. maculatus. A clearer understanding of the consequences of the osmorespiratory compromise at the whole-animal level relies on further examinations of the interplay between salinity and oxygen across stenohaline and euryhaline species and across acute and chronic exposures.

Cadmium‐induced changes in haemato‐immunological, oxidative stress and antioxidant parameters of Cyprinus carpio: Protective role of curcumin

Thu, 12 Mar 2026 07:34:51 -0700

Abstract

This study examined the adverse effects of sublethal concentrations of cadmium (Cd) and the potential of curcumin (CUR) to mitigate Cd-induced toxicity. We administered 1.5 and 3 mg/L of Cd and 100 mg/kg of CUR to fish (Cyprinus carpio) separately and in combination over 14 days. At the end of the experiments, various haematological and immunological parameters, oxidative stress levels and antioxidant parameters of fish were measured, and the differences between the groups were evaluated. Simultaneous CUR treatment with Cd reversed the changes in haematological parameters in fish, increased immune responses, reduced oxidative stress and normalized the impaired antioxidant enzyme activities. In summary, our study showed that dietary supplementation with CUR may be an effective strategy to reduce the toxic effects of Cd in carp.

Evidences of sibling bites in porbeagle shark (Lamna nasus) embryos

Juan M. Piscicelli, Karina A. Arias, Gustavo E. Chiaramonte — Tue, 10 Mar 2026 02:49:24 -0700

Abstract

The porbeagle, top predator with amphi-temperate, coastal and oceanic distribution, ranges 26–57°S in the Southwest Atlantic. An injured, pregnant female was found stranded on the coast of Quequén, with two male embryos in each uterus. The embryos in the right uterus differed in size, and the smaller one had injuries. Our hypothesis is that embryos have the ability to perform lateral movements that allow them to bite obliquely along the anteroposterior axis of the uterine sac, so that the lacerations of the smaller embryo would be the result of lateral bites from its sibling, as the latter would not have space to attack it in a more dangerous way.

Oxygen supply capacity across early‐life stages in common snook Centropomus undecimalis

Christina J. Welsh, Kevan L. Main, Brad A. Seibel — Tue, 10 Mar 2026 02:34:44 -0700

Abstract

Estuaries supply a critical habitat to many ecologically and commercially valuable fish species, providing safety and food availability during the larval and juvenile stages. However, dissolved oxygen is naturally dynamic in these systems, varying from complete anoxia to hyperoxia. In some species, the larval stage may be particularly vulnerable to low-oxygen stress due to incomplete development of oxygen transport systems, high metabolic cost associated with early feeding and a narrow aerobic scope to support additional activity. Increasing seawater temperatures further increase oxygen demand in poikilothermic species and are amplified in shallow inshore habitats. In teleost fish, estuarine hypoxia and warming may lead to recruitment bottlenecks at the larval stage, which often requires a narrower range of environmental conditions than juveniles or adults. Here, we compared the physiological oxygen supply capacity (α) and aerobic scope of late-larval and early-juvenile common snook Centropomus undecimalis (Bloch 1792), a coastal marine species found in the Gulf of Mexico, Caribbean and western Atlantic from Florida to Brazil. We hypothesized that larvae would be more hypoxia sensitive than juveniles but instead found that routine and maximum metabolic rates scaled similarly with body mass, resulting in size independence of factorial aerobic scope and critical oxygen partial pressure between life stages. The α value matched maximum demand across the transition from larval to juvenile stages, suggesting that C. undecimalis can effectively regulate the supply of oxygen from the environment to their tissues as early as 17 days post hatching. Additionally, C. undecimalis exhibited a P _cmax value of 18.63 kPa, indicating that their full aerobic potential can be met only at oxygen pressures near air saturation. Although this is the expected P _cmax based on their previously reported prevalence in surface waters, this may lead to reduced habitat availability as estuarine deoxygenation worsens in the Gulf of Mexico.

A new catfish species of Microcambeva Costa & Bockmann, 1994 (Siluriformes: Trichomycteridae) from southern Brazil, with a redescription of M. ribeirae Costa, Lima & Bizerril, 2004

Sun, 08 Mar 2026 05:25:41 -0700

Abstract

Among the few species of Microcambeva reported as occurring in more than one hydrographic basin, M. ribeirae has been previously listed from both the Ribeira de Iguape and the Guaraqueçaba basins. However, morphological and molecular analyses revealed that the specimens from Guaraqueçaba represent a new species, which is described in this study. Therefore, the distribution of M. ribeirae is restricted to the Ribeira de Iguape basin, and this taxon is redescribed. The new species is the southernmost record of the genus and is diagnosed among congeners by the T-shaped dark blotch in the dorsal portion of the head in preserved specimens. It is distinguished from most congeners, except for M. bendego and M. ribeirae, by the lack of a filamentous first pectoral-fin ray. Distinguished from the latter species by having only five pre-caudal vertebrae, the tip of the hyomandibula reaching the vertical through the anterior tip of the preopercle, and the last anal-fin ray branched. Molecular analysis of the cytochrome c oxidase subunit I (cox1) mitochondrial gene including most species of Microcambeva (except M. draco) supports the close relationship of the new species with M. ribeirae. The two species are nonetheless genetically different, with a 2.2% molecular distance. The conservation status and biogeography of the new species and of M. ribeirae are discussed.

Speciation of European bullheads (Cottus spp.): The next problem for taxonomy of northern freshwater fishes

David S. Murray, Vladimír Kováč, David Wright, Gordon H. Copp — Fri, 06 Mar 2026 05:04:07 -0800

Abstract

High morphological and ecological diversity displayed by European bullheads led Freyhof et al. (2005) to describe 15 nominal species. However, the basis for declaring these nominal species is contentious due to a lack of rigorous statistical analysis of morphological variations among populations, limitations in the inferences made from previous generations of molecular studies, a dearth of next-generation sequencing tools for European bullheads and an underestimation of the complexity of evolutionary processes. Here, we argue that the current evidence is insufficient for accurate speciation of European bullhead into the nominal species proposed by Freyhof et al. (2005). We suggest that future studies incorporate analytical approaches such as chromosome-level reference genomes, integration of multiple biological data sources into multispecies coalescent models and rigorous statistical analysis of the full range of morphological characters, both meristic and mensural. Furthermore, we highlight the necessity of incorporating a standardised conceptual framework while considering bullhead speciation, as well as some practical suggestions of what such a process would look like.

Microanatomical characterization and histochemistry of the Siamese dwarf rasbora, Trigonostigma somphongsi (Meinken, 1958), a critically endangered species in Thailand: Implicating to the conservative biology

Fri, 06 Mar 2026 04:31:21 -0800

Abstract

The fundamental organization of fish tissue is crucial to bridge the fields of histopathology and physiology throughout research on biology. This study examines tissue examination of the Siamese dwarf rasbora, Trigonostigma somphongsi (Meinken, 1958), a critically endangered freshwater fish in Thailand. All fish were obtained from the freshwater area in Nakhon Nayok Province, Thailand, and were then processed using the standard histological and histochemical methods. Our observation clearly provides a detailed histological pattern of the major systems. Interestingly, the oral cavity had three distinct regions based on the presence of a taste bud, a mucous secreting cell and a longitudinal fold in the anterior, middle and posterior regions, referring to the digestive function. Moreover, the mature gonads (mature oocytes and spermatozoa) from all fishes indicate the adult stage. It is noted that this is a foundation of reproductive success under a biological life history, which is implicated to protect the area-based conservation during the rainy season. This study uses a histological approach to provide information related to the systematic functional and anatomical phenomenon of T. somphongsi throughout the basic information for the effective area-based conservation.

Effect of structural connectivity on the assemblage diversity patterns of central Mexico icthyofauna

Fri, 06 Mar 2026 04:20:33 -0800

Abstract

The complex hydrographic history of central Mexico can explain the phylogeographic patterns of endemic freshwater fish; nevertheless, the process that determines the assemblage patterns has been poorly studied. Here, we evaluated the freshwater fish diversity patterns of central Mexico through the estimation of α-diversity and taxonomic and phylogenetic β-diversity indices calculated from geographical distribution records and a time-calibrated phylogenetic tree. Furthermore, the effects of isolation by distance and isolation by climatic and hydrographic resistance on the turnover of species were evaluated at different temporal scales. The results suggested that the Chapala region was the most diverse area, with phylogenetic overdispersion. Geographical distance and climatic and hydrographic components played important roles in freshwater fish assemblage patterns within the region. Our findings demonstrated the relevance of the assessment of taxonomic and phylogenetic diversity, considering the temporal context of the landscape, in explaining patterns and suggesting conservation strategies. Because the variation in diversity was explained mainly by environmental gradients, conservation efforts would ideally protect enough sites to capture this entire gradient.

Insights into the structure of grey reef shark aggregation, Carcharhinus amblyrhynchos (Bleeker, 1856), in two distinct channels of the Maldivian archipelago, Indian Ocean

Tue, 03 Mar 2026 00:00:00 -0800

Abstract

The grey reef shark Carcharhinus amblyrhynchos is one of the most frequently encountered reef-associated shark species in the Maldives, yet very little is known about its local size structure or population dynamics. This study provides new insights into two aggregations of C. amblyrhynchos in the Maldives, based on biometric measurements obtained with laser photogrammetry, standardized visual surveys, opportunistic behavioural observations, and video analyses of citizen science data spanning 2013–2024. In particular, between 2022 and 2023, biometric data and visual observations from two distinct sites, Villingili Kandu in North Huvadhu Atoll and Miyaru Kandu in Vaavu Atoll, were collected to preliminarily characterize the composition of these aggregations and to provide information on the ecology of grey reef sharks. The results revealed a pronounced female-biased sex composition and occurrences of mating in both channels, as well as a potential nursery area in Miyaru Kandu. Combining these data with predation and cleaning events recorded, we suggest that these channels might constitute important key habitats for grey reef shark aggregations. Laser photogrammetry data from 353 individuals were analysed, and a robust relationship between pre-caudal length and total length (R ² = 0.97) was established, enabling the derivation of a correction index through linear regression to predict and enhance the accuracy of size estimates. Finally, long-term video records demonstrate that Villingili Kandu currently hosts the largest documented aggregation of C. amblyrhynchos in the Maldives. These initial findings provide a baseline for further studies on the drivers influencing the aggregations of this species and its life history within the archipelago.

Individual variability in activity patterns in Atlantic halibut (Hippoglossus hippoglossus) revealed using pop‐up satellite tags

Fri, 27 Feb 2026 18:56:32 -0800

Abstract

Understanding fish behaviour and activity patterns is essential for interpreting their ecology and the processes that shape population dynamics, yet such information remains limited for wild fishes because observing individuals in situ is challenging. Recent technological advances make it possible to collect high-resolution movements and activity data over extended periods, opening the door to detailed descriptions of fine-scale behaviours and their temporal variability. We evaluated the coarse and fine-scale activity patterns of 25 Atlantic halibut (Hippoglossus hippoglossus) individuals throughout a complete seasonal cycle in the Gulf of St. Lawrence using acceleration data at a resolution of 5 s extracted from 25 pop-up satellite archival tags (PSAT). We sought to classify individuals into behavioural contingents within the population and to identify specific behaviours that could be identified with the fine resolution of the available data using dynamic factor analysis, visual representations and variance partitioning. Despite some common general patterns of activity during reproduction, the data were characterized by a high level of individual variability in the amount and patterns of activity, with each halibut exhibiting a unique activity profile across the year. Periodic daily behaviours (diurnal and nocturnal) were identified for several individuals but with no clear pattern in their recurrence over time within individuals or coherence between individuals. Overall, individual variability in activity dominated over the common patterns detected, with little evidence of distinct activity contingents among individuals. The high-frequency activity data available from PSATs in this study challenge the traditional view of halibut and flatfish in general, as passive bottom dwellers exhibiting simple, perhaps periodic behaviours, instead supporting growing evidence that fish exhibit substantial individual behavioural differences.

A new, conspicuously pigmented Pyrrhulina (Teleostei: Characiformes: Lebiasinidae) from the Río Tigre, Loreto, Peru

Fri, 27 Feb 2026 18:46:07 -0800

Abstract

A new species of Pyrrhulina is described based on morphological and molecular evidence. Pyrrhulina punctata is distinguished from all congeners by the presence of a series of 7 to 16 irregular blotches of dark pigmentation on the flanks, equally marked in juveniles and adult specimens, the presence of 26–28 lateral-line scales, 17–21 maxillary teeth, 23–25 outer premaxillary teeth, 40–41 inner premaxillary teeth and 23 outer dentary teeth, the distinctly elongate rays on dorsal, pelvic and anal fin on adult males, the presence of irregular dark marks on the basal portion of anal-fin rays and intervening membranes, and the presence of a second dark blotch on the distal tip of longest dorsal-fin rays. The molecular data indicate a closer relationship with Pyrrhulina spilota, corroborating the morphological evidence and the shared colouration pattern. Besides the diagnostic characters allowing the recognition of both species, their distinction was corroborated by all species delimitation algorithms [Assemble Species by Automatic Partitioning (ASAP), Poisson Tree Processes (PTP) and Generalized Mixed Yule Coalescence (GMYC)] employed herein. In addition, the occurrence of P. spilota in the Madeira basin is refuted as the registers were based on misidentifications of Pyrrhulina vittata.

Familiarity among kin has minor effects beyond grouping for escape response in a shoaling fish

Fri, 27 Feb 2026 02:10:34 -0800

Abstract

Prey have evolved cost-effective antipredator manoeuvres to evade predators, and living in a group is a common strategy employed to improve survival. Associating with familiar conspecifics, particularly kin, may further enhance these strategies by improving the flow of reliable information concerning the type and magnitude of nearby threats. This study investigated the influence of familiarity among shoalmates on the activity and escape responses of a shoaling damselfish. We examined the routine swimming and fast-start response of juvenile spiny Chromis (Acanthochromis polyacanthus, Bleeker 1855) when tested alone, with familiar kin, or with unfamiliar conspecifics. Solitary fish were less active, moved more slowly than fish in groups and were more likely to exhibit a substantially delayed (>0.05 s) fast-start response to a startle stimulus. Fish with familiar kin exhibited the highest escape speeds and travelled the greatest distances during the initial response, and there was a trend for familiar fish to perform better than non-familiar fish. Interestingly, the time taken to initiate a response (response latency: ~0.01 s) for those undertaking a non-delayed fast start was unaffected by treatment. Shoaling with familiar kin enhanced some key aspects of the fast-start escape response, which may contribute to predator confusion effects and increase the likelihood of survival for individuals within familiar groups.

Mobile cleaning stations: trevally scrape on sharks in a tropical reefscape

Nico Fassbender, Isobel B. Sewell, Robert W. Bullock, Jessica J. Meeuwig — Fri, 27 Feb 2026 02:05:47 -0800

Abstract

Inter-species scraping has been reported between sharks and some teleost fish species to reduce ectoparasite loads and thereby increase fish health in an otherwise featureless pelagic environment. Here we report observations of interspecific scraping behaviour in reef environments between three species of trevally and three species of shark in the Seychelles Archipelago. These include the first scraping interactions for bull sharks Carcharhinus leucas and tiger sharks Galeocerdo cuvier observed in the wild. The interactions occurred despite the availability of cleaning stations and rough substrates suitable for self-scraping. These observations further our understanding of inter-species cleaning relationships in reef-associated fish and sharks, and suggest that sharks may play a role in supporting reef fish health.

A new Hyphessobrycon (Characiformes: Acestrorhamphidae) of the Hyphessobrycon agulha lineage of Hyphessobryconinae from the lower Aripuanã basin, Brazil, with comments about the lineage

Thu, 26 Feb 2026 23:04:25 -0800

Abstract

A new species of Hyphessobrycon is described from a tributary of Rio Jatuarana, lower Rio Aripuanã basin, Rio Madeira basin, Apuí, Amazonas. The new species is part of the Hyphessobrycon agulha lineage, with the typical midlateral narrow black stripe immediately followed dorsally by an iridescent stripe. Its phylogenetic position is corroborated by the DNA barcoding methodology, which also indicates the new species as closely related to Hyphessobrycon ericae and Hyphessobrycon ribeiroi, with both possessing very distinct colour patterns. The new species can be distinguished from all species of Hyphessobrycon by the association of a well-defined and horizontally elongated humeral blotch with a ventral diffuse expansion, a conspicuous caudal peduncle blotch restricted to the ventral half of the caudal peduncle and proximal half of mid rays of caudal fin, the presence of a red midlateral stripe dorsal to the iridescent stripe and lateral-line scale counts.