Journal of Fish Biology

Noise pollution is an increasing threat to soniferous fishes, however, research on noise pollution impacts is limited to few species and rarely studied in situ. Red Drum (Sciaenops ocellatus) is an estuarine, fishery species that choruses during spawning. We tested predictions of the hypothesis that Red Drum alter sound production in response to vessel noise. We used passive acoustic monitoring in 2021 and 2022 at an estuarine inlet and Generalized Least Squares (GLS) models to assess vessel sound exposure levels over time (SEL) and other abiotic parameters on Red Drum chorus SELs. GLS models of daily crepuscular choruses indicated a >5% reduction in proportion to crepuscular vessel noise in 2021. GLS models testing influence of abiotic variables and prior vessel noise, predicted reduced chorus SELs proportional to prior noise SEL: ca. 5% and 3% of vessel SEL in 2021 and 2022, respectively. In some instances, SEL during vessel noise was lower than fish chorus SEL immediately prior, indicating instances when fish reduced chorus amplitude during vessel noise or fled the immediate area. In cases when SEL of vessel noise periods exceeded fish calling SEL immediately prior, it is not known if fish modulated calling amplitude because the portion of combined vessel noise and fish chorus amplitude from vessels is unknown. In peak spawning season (September-October) vessel noise was frequent, detected in >31% of recordings in both years and up to 100% of recordings on some dates. Observations of disrupted choruses and high vessel noise prevalence suggest spawning behavior may be impacted by abundant vessel noise.

Uncontrolled carbon dioxide emissions from human activities contribute to ocean warming and acidification. These alterations in ocean chemistry threaten marine organisms, such as the true giant clam, Tridacna gigas, which is already imperiled due to overharvesting and habitat destruction. To gain an understanding of the physiological and molecular responses of T. gigas and its symbiotic dinoflagellates to ocean warming and acidification, we subjected juvenile individuals to different treatments simulating predicted seawater pH (7.6 and 8.0) and temperature (28{degrees}C, 30{degrees}C, 32{degrees}C and 34{degrees}C) levels for the next century. Juvenile giant clams were able to tolerate sustained exposure to temperatures of up to 32{degrees}C and pH as low as 7.6, while exposure to higher temperature (34{degrees}C), regardless of pH level, resulted in total mortality after a week. However, symbiosis was compromised even in the sublethal treatments, as indicated by the decrease in Symbiodiniaceae density and changes in symbiont gene expression. Symbionts significantly upregulated genes involved in splicing, translation, fatty acid metabolism, and DNA repair, which may constitute an adaptive response, while downregulating genes involved in photosynthesis and transmembrane transport, suggests impaired transfer of photosynthates to the host. These findings demonstrate the vulnerability of the juvenile T. gigas holobiont to heat stress, highlighting the critical importance of continued conservation and management alongside efforts to mitigate global changes in ocean conditions to safeguard this iconic marine bivalve. Summary StatementThis study investigates physiological and molecular responses of Tridacna gigas to seawater warming and acidification, providing insights into the potential future of endangered giant clam populations in a changing ocean.

AimTo assess how biogeographic barriers and environmental heterogeneity shape connectivity and local adaptation in the striped Venus clam (Chamelea gallina), a commercially exploited bivalve in the Mediterranean Sea. LocationNortheast Atlantic (Gulf of Cadiz) and Mediterranean Sea (Alboran, Balearic, Tyrrhenian and Adriatic regions). TaxonChamelea gallina (Bivalvia: Veneridae). MethodsWe analysed genome-wide single nucleotide polymorphisms (SNPs) from 226 individuals sampled across six regions (Gulf of Cadiz, Alboran Sea, Balearic Sea, Ebro Delta, Tyrrhenian Sea and Adriatic Sea) using a seascape genomic framework. Population structure was inferred using both putatively neutral and adaptive loci. Genotype-environment associations were tested against key oceanographic variables, including sea surface temperature, salinity and nutrient availability. ResultsNeutral loci revealed weak genetic differentiation, consistent with substantial gene flow across most of the species range. In contrast, putatively adaptive loci uncovered pronounced genetic structure that corresponded closely to major Mediterranean biogeographic regions, particularly the Adriatic Sea, the Gulf of Cadiz and western-central Mediterranean basins. Significant associations were detected between genetic variation and environmental gardients, with several candidate adaptive SNPs located within coding regions, suggesting functional responses to spatially heterogeneous conditions. Main conclusionsOur results demonstrate that local adaptation can generate biologically meaningful population structure in C. gallina despite high levels of connectivity inferred from neutral markers. This decoupling between neutral and adaptive variation highlights the importance of integrating adaptive genomic information into biogeographic inference. Recognizing environmentally driven genetic differentiation is essential for defining robust management units and for improving the long-term sustainability and resilience of C. gallina fisheries under increasing anthropogenic pressure and climate change.

BackgroundPacific saury Cololabis saira is one of the important food resources drawing attention for its recent rapid decline of catch. Their life cycle and embryonic development have been largely unknown. It is important to clarify how the habitat and reproduction of this species have been affected by the global changes of aquatic environment. ResultsWe obtained fertilized eggs of C. saira, by spontaneous spawning and artificial fertilization, and observed the embryonic development up to larval stages. Embryonic stages are documented with major periods of developmental events; cleavage, gastrulation (epiboly) and somitogenesis and organogenesis. Remarkably, segmentation of somites starts in the middle of epiboly, unlike other well-documented teleost species such as zebrafish and medaka. Morphological changes in larval stage up to feeding juvenile is also described. Growth speed of larval Pacific saury is dramatically rapid, in comparison to closely related beloniform fish such as medaka. ConclusionsIn comparison to medaka, early embryogenesis of saury proceeds slowly, although being followed by early onset of somitogenesis. This might be partly responsible for the rapid growth into adult (larger than 20 cm in body length) in only half a year. Further studies on embryonic development will uncover the molecular mechanisms underlying the characteristics of Pacific saury as an excellent source of nutrition and as an indicator of major environmental changes such as global warming.

Hypanus brevis (Garman, 1880) and Hypanus dipterurus (Jordan & Gilbert, 1880) are currently considered as a conspecific lineage of the "diamond stingray" from the Eastern Pacific. This taxonomic group has been the subject of nomenclatural disputes for about 145 years. To clarify the historical confusion surrounding this lineage, we employed an integrative taxonomic approach using specimens from the Eastern North and Eastern South Pacific (ENP and ESP). The genetic results, based on single and multilocus mitochondrial analyses, revealed a distinct evolutionary unit in the ESP. While morphological analyses detected subtle differences between ENP and ESP specimens, most characters exhibited significant overlap (e.g., disc shape, dentition patterns, body coloration), suggesting low evolutionary divergence. A calibrated molecular clock analysis estimated this divergence at approximately 3.09 Ma. In accordance with Garmans (1880) original description based on specimens from Paita (northern Peru), we formally resurrect H. brevis from synonymy with H. dipterurus. Our findings suggest an anti-tropical speciation pathway, with core populations of H. brevis and H. dipterurus restricted to the temperate waters of the ESP and ENP, respectively. Notably, a single, fixed COI haplotype was detected in all H. brevis specimens from the north-central Peruvian coast. This result may indicate a severe bottleneck event, raising concerns about the genetic health and long-term viability of this vulnerable species. Finally, we analyzed historical fishery data of H. brevis to infer its current population status, suggesting targeted conservation measures and precautionary management to prevent further loss of genetic diversity.

Many commercially exploited fish stocks have declined over the last few decades. It is therefore essential to identify natural populations and understand local adaptation for sustainable management. Salinity is a key environmental factor shaping local adaptation, and adaptive trait divergence often occurs at the egg and larval stages. The strong salinity gradient in the brackish Baltic Sea has driven rapid adaptation in multiple taxa. The Eastern Baltic cod (Gadus morhua) has adapted to low salinity with buoyant and tolerant eggs and larvae, but the stock has declined both in abundance and geographical range during the last decades. The main reproduction area of this stock is in the Bornholm Basin (ICES subdivision (SD) 25) in the southern Baltic Proper. Cod in this area, however, exhibit stunted growth and small body sizes. In contrast, large and healthy cod in reproductive condition have been observed in the [A]land Sea in the northern Baltic Proper (SD 29), raising the question of whether these fish represent a locally adapted population capable of successful reproduction in the lower salinities (5-10 psu in the northern Baltic Proper (SD 27, 29 and 32). Here, we experimentally assessed egg and yolk-sac larvae survival across salinities, egg size, egg and larval neutral buoyancy and egg survival on sediment, to test whether northern ([A]land) cod show adaptation to low salinity at early life stages as compared to southern cod. Mortality of larvae increased with decreasing salinity in cod from both areas, with the lowest survival at 7 psu. At 9 psu, more than 50% of northern cod larvae survived, suggesting that development could occur in SD29. Egg size and buoyancy were similar between northern and southern cod, and eggs and larvae were negatively buoyant, sinking under local salinity conditions. Nevertheless, the eggs survived and hatched well on sediment, indicating potential for demersal spawning. Our findings show no strong evidence of adaptive divergence to lower salinity in northern cod; however, their ability to tolerate sediment contact at early life stages suggests that Eastern Baltic cod may reproduce outside their historical spawning grounds.

AO_SCPLOWBSTRACTC_SCPLOWMigration events can act as strong selective filters by spatially sorting individuals according to their migration ability, behaviour, and associated functional traits. The European eel, a panmictic and threatened fish, presents various estuarine migration patterns at juvenile stage (glass eel), ranging from sedentarization in brackish/saltwater of the estuary (non-migrant phenotype) to upstream colonisation of freshwater ecosystems (migrant phenotype). We hypothesize that migration propensity is partly genetically determined in glass eel, and that migration-related genotypes are spatially sorted during estuarine migration. To test these hypotheses, we first collected six pools of individuals over three years at two extreme sites along a gradient from ocean to Adour River tidal limit (Ocean vs. Upstream). Secondly, we collected additional glass eels and phenotypically sorted migrant vs. non-migrant individuals using an experimental device mimicking alternating tidal currents, producing two other pools. Whole genome pool sequencing and analysis of these eight pools generated 18.99 106 SNP variants. Controlling for linked selection through a local score approach, we found five best outlier SNPs with a significant genetic differentiation between Ocean vs. Upstream sites (average FST = 0.21) compared to the pangenomic estimate (FST = 0.0086). These five SNPs were all found in the same gene (gpb2), involved in interferon-mediated antiviral immune responses. We also found 28 best outlier SNPs with a significant genetic differentiation between migrant vs. non-migrant phenotypes (average FST = 0.51). They were located in genes mainly involved in neuronal development, cell migration and tissue remodelling, transcriptional regulation, and metabolic or stress-related processes. Our results support that variation in eel migration propensity is partly genetically determined and that, while panmixia maintains high level of genetic diversity, spatial sorting could promote intra-generational genetic divergence between habitats of European eels. However, the absence of shared genes among the best outliers between in-situ and experimental contrasts suggests a complex and context-dependent genetic control of migration.

The evolution of body shape reflects the interplay between functional constraints and habitat structure. In fishes, cave environments are well known for promoting regressive traits such as eye and pigment loss, yet their influence on overall body form remains poorly understood. Here, we examine patterns of body shape variation in cave- and surface-dwelling trichomycterid catfishes from northeastern Colombia to assess whether consistent associations exist between habitat type and morphology. Using geometric morphometric analyses, we quantified differences in body shape among species inhabiting subterranean and surface environments. Our results reveal significant habitat-associated differentiation in body shape along the main axes of morphological variation. Cave-dwelling species exhibit more elongated and fusiform body shapes, whereas surface-dwelling species tend to show deeper and more robust morphologies. In a functional context, these contrasting body patterns suggest associations with differing locomotor demands imposed by subterranean versus surface habitats. Although we do not explicitly test convergence or performance, the recurrence of similar body shapes among species from different clades occupying comparable habitats is consistent with repeated morphological responses to shared ecological constraints. Research HighligthsO_LIMultivariate shape analyses reveal significant habitat-associated variation in trichomycterid fishes. Recurrent morphological patterns suggest repeated responses potentially mediated by habitat constraints. C_LIO_LIBody shape differs consistently between cave- and surface-dwelling trichomycterids. Cave species exhibit more elongated and fusiform forms, whereas surface species display deeper body configurations. C_LI

Pacific cod is a key species in North Pacific fisheries, and its stock assessment and management units are separated according to biological, geographical, and administrative information. Understanding the fine-scale genetic population structure of this species is crucial for effective management, particularly in regions such as Japan, where complex coastal geography and localised fisheries management prevail. Therefore, in this study, we analysed genome-wide single nucleotide polymorphisms (SNPs; 6,035 loci) in 496 individuals of Pacific cod sampled from 33 sites around the Japanese archipelago via genotyping by random amplicon sequencing-direct (GRAS-Di) analysis. Our analyses revealed three major genetic groups: Japanese Broad Range, Northernmost Honshu-Hokkaido (NHH), and Western Sea of Japan groups. These groups exhibited significant genetic differentiation (global FST = 0.056), distinct levels of nucleotide diversity, and group-specific genome-wide patterns of Tajimas D. Moreover, demographic history reconstruction based on whole-genome sequencing of three representative individuals revealed that each genetic group followed distinct demographic trajectories since the last glacial period. Importantly, the NHH group, related to the Mutsu Bay spawning aggregation and previously shown to exhibit strong natal homing in tagging surveys, was genetically identified for the first time in this study. Isolation-by-distance was observed across Japanese waters and within the Japanese Broad Range group, but not within the NHH group, suggesting that gene flow is generally restricted by geographic distance, except within the NHH group. To evaluate the potential for genetic stock identification, we extended a resampling-based cross-validation framework by incorporating outlier detection to assess marker selection strategies. Over 500 background SNPs were required to achieve >90% assignment accuracy for genetic stock identification, whereas only eight or more outlier SNPs showed comparable performance. These findings suggest that carefully selected SNP panels, particularly those including outlier loci, substantially improve stock discrimination. Overall, our study demonstrates the fine-scale genetic structure and demographic history of Pacific cod in Japanese waters and highlights the utility of practical marker strategies for enhancing the biological realism of fisheries assessment and supporting sustainable fisheries management.

Sea star wasting disease has caused widespread mortality in the kelp forest predator, the sunflower sea star (Pycnopodia helianthoides). Wild populations have declined by up to 99% in parts of their native range along the western North American coast. In response, a multi-institutional conservation breeding and rearing program has been initiated to support future reintroduction efforts for the species. We split a full-sibling cohort across four larval density treatments (1 larva/ml, 2 larvae/ml, 5 larvae/ml, and 15-20 larvae/ml) to assess the effects on larval settlement, juvenile survival, and juvenile fitness at 12 months old. Stars raised in the highest density treatment displayed a lower settlement rate and were significantly smaller than the other density groups at 12 months old, but showed no significant difference in flip time, a measure of fitness. Additionally, measurements of diameter, weight, and arm count across modern and historical juvenile and adult stars indicate that P. helianthoides experience exponential weight gain as they grow in length, with corresponding asymptotic growth in arm count. These findings will inform best practices for the aquarium propagation of P. helianthoides and will contribute to broader efforts aimed at reestablishing populations in the wild.

Climate warming alters the thermal environment experienced by ectotherms, whose physiological performance and fitness are constrained by temperature. Early life stages are often the temperature-sensitive phases of the life cycle, with potential consequences for population persistence, particularly in freshwater stenotherms such as the Arctic charr (Salvelinus alpinus). The persistence of populations will partly depend on the adaptive potential of critical life stages to environmental changes. In this study, we used a common garden approach to compare the response and phenotypic plasticity of four charr populations to warmer conditions. These populations inhabit thermally contrasted lakes and differ in origin (native/introduced) and management history. We reared embryos at either an optimal (5{degrees}C) temperature for larval development or a warmer but realistic (8.5 {degrees}C) temperature. We tested adaptive divergence among populations in four traits (survival, incubation duration, body length and yolk sac volume), using Qst - Fst comparisons. We report negative effects of temperature on body size, survival and earlier hatching. Thermal reaction norms differed among populations, indicating adaptive divergence. Contrary to expectations, populations originating from warmer environments did not consistently exhibit higher trait values under elevated temperatures. In contrast, the unmanaged and colder high-altitude population exhibited higher survival rates and lower yolk reserves for a given size under heat stress than the other populations. Our results suggested that evolutionary trajectories specific to each population are shaped by factors related to the populations history, including introductions, demographic fluctuations and long-term repopulation practices, which can jointly influence the potential for adaptation to heat stress.

Sea turtles exhibit environmental sex determination and face risks of over-feminization, heat-induced embryonic failure, and hatchling mortality due to rising global temperatures. Mitigating these impacts of climate change may necessitate interventions to reduce sand temperature. One proposed strategy is to irrigate nests with seawater, but uncertainties exist regarding turtle egg tolerance to saline nest sand. To test the hypothesis that sea turtle embryos can tolerate a regimen of irrigation with seawater at a management-relevant scale, we investigated the impact of two levels of large-scale irrigation using cooled seawater on green turtle nests and embryos, assessing the effects on important nest environmental factors and developmental success. Irrigation which simulated 200 mm of rain reduced the temperature in clutches by up to 5.6 {degrees}C (1.34 {+/-} 0.10 mean {+/-} SD) without adversely affecting clutch oxygen levels, sand water potential, or sand moisture content, but our irrigation regimens resulted in very low hatching success (1.5%). However, late-stage embryonic mortality predominated, suggesting that early embryos may have an unexpected tolerance to saline sand and increasing our understanding of sea turtle resilience to seawater irrigation. The observation that younger embryos may be less susceptible to seawater-associated mortality than mature embryos near hatching further informs the limitations and potential applications of seawater irrigation as a management strategy.

Sarita Lake, British Columbia houses a distinctive population of threespine stickleback (Gastrosteus aculeatus L.) with a phenotype characterized by unusually large individuals relative to nearby conspecifics. We tested the hypothesis that members of this population are not isometrically larger but rather exhibit variation in allometric trajectories that reflect changes in developmental timing impacting the developmental-genetic architecture of the phenotype. We used 3D geometric morphometrics to characterize the size and shape of skulls, pectoral girdles and pelvic girdles from a sample of individuals from nearby freshwater and marine populations and compare them to a sample from Sarita Lake. We showed that individuals from the Sarita Lake population are larger in each body region compared to most other populations examined. Further, these individuals have dorsally expanded skulls and relatively robust pelvic armour. We also showed that the relationship between size and shape is differently structured among body regions and is heavily influenced by non-uniform sexually-mediated variation across populations sampled. Our results reflect complex underlying developmental trajectories, and we suggest that the large phenotype observed may be driven by fecundity selection on female size in combination with a limnetic trophic niche and relatively increased predation pressure in Sarita Lake.

We provide a detailed description of embryonic development in the convict cichlid (Amatitlania nigrofasciata) from fertilization to hatching at 26 {degrees}C, together with a practical staging table anchored to established teleost reference frameworks. Fertilized eggs were obtained by both natural spawning and artificial fertilization. Unfertilized eggs were ovoid and adhesive, surrounded by a chorion and a sticky mucous layer. Early development proceeded, in broad outline, through the teleost sequence of meroblastic discoidal cleavage, blastula, gastrula, segmentation, and organogenesis. The first cleavage occurred at 1.75 hours post-fertilization (hpf), with subsequent cleavages at 30 min intervals, reaching the 64-cell stage at 4.25 hpf. Cleavage up to the 64-cell stage progressed on a timescale broadly comparable to that reported for other cichlids, whereas the interval from the 64-cell stage to early epiboly was relatively short in this species. The high, sphere, and dome stages occurred at 8, 9, and 10 hpf, respectively, with epiboly initiating at the dome stage. At the dome stage, a marginal thickening interpreted as the presumptive embryonic shield became apparent. During early epiboly, the blastoderm showed pronounced spatial heterogeneity: it was consistently thicker and advanced more rapidly on the prospective embryonic axis side, yielding a readily detectable asymmetry. A morphologically distinct embryonic axis became visible at 40-50% epiboly, and epiboly was completed at 28.5 hpf. Notably, somitogenesis began before epiboly completion (first somites at 85-90% epiboly), indicating temporal overlap between late gastrulation and early segmentation. Major organ primordia became apparent during the overlapping segmentation/organogenesis interval, and hatching occurred around 70 hpf. Newly hatched larvae possessed three pairs of adhesive glands. This staging reference enables reproducible developmental sampling and should facilitate future comparative, mechanistic, and experimental work using the convict cichlid.

Understanding behavioral differences between non-native and closely related endangered species could be important to aid conservation management. In volume 169 of Zoology, Bels et al. (2025) reported on their comparison of display-action-patterns (DAP) between native Iguana delicatissima and non-native iguanas present on islands of the Guadeloupe Archipelago in the Caribbean Lesser Antilles. Here, we address conceptual and methodological concerns about their work and reanalyze their data given our proposed corrections, primarily a literature-informed adjustment of their "species" category. We additionally utilize online videos from South American mainland I. iguana populations, from where the non-native iguanas in the Guadeloupe Archipelago originate, to better understand the different DAPs between native and non-native iguanas in the Guadeloupe Archipelago. Significant differences in DAP characteristics among "species" categories (native I. delicatissima, non-native iguanas, and hybrids) show that Bels et al. (2025) oversimplified their data analyses by merging all non-native populations into one group. This result indicates the presence of behavioral variation among subpopulations within widely hybridizing iguanid populations, which has been poorly studied. Additionally, videos from mainland populations across two major mitochondrial clades of Iguana iguana show that non-native iguanas on Guadeloupe retained DAP characteristics of those populations from which they originate. We discuss these findings in light of the proposed hypotheses put forward by Bels et al. (2025), of which two can be excluded. Overall, our reanalysis shows that studies focusing on characteristics within settings of complex hybridization in diverse species should acknowledge this complexity.

Incilius marmoreus inhabits an extensive range along the Pacific Coast of Mexico and a smaller allopatric region in the State of Veracruz, exhibiting an unusual distribution among herpetofauna. Gunther (1901) classified the Pacific coastal toads Bufo argillaceus and B. lateralis as conspecific with Incilius [Bufo] marmoreus, which has its type locality in Veracruz. Here, we adopt a multidisciplinary approach to reevaluate the phylogeography and taxonomy of I. marmoreus by gathering and analyzing morphological data and conducting phylogenetic and population genetic analyses from genome-wide SNP data. Our results uphold the current taxonomy by concurring with Gunther (1901). Our phylogenetic and population genetic analyses suggest that I. marmoreus from Veracruz are closely related to those from Oaxaca whilst coalescent analyses recovered a north-south split along the Pacific Coast estimated to have occurred [~]0.86 Mya followed by a shallow east-west split in the southern lineage that separates the Pacific coastal populations and the allopatric population in Veracruz [~]0.33 Mya. This species displays marked morphological and genetic diversity throughout its range, but this variation appears to be consistent with gene flow across contiguous populations rather than the existence of independent evolutionary lineages. The processes leading to the geographic isolation of the population on the coast of Veracruz remain uncertain, but we hypothesize that climatic and vegetation changes in the Late Pleistocene may have played a role.

Recently, an inventory of genes in phytoplankton was conducted through expeditions such as TARA Oceans. Approximately 1.5 million genes were identified, of which at least three-quarters have unknown function. Presently, a several research programmes are engaged in the sequencing of marine biodiversity, resulting in a rapid expansion of genomic databases. Access to the genomic sequences of these organisms will soon be readily accessible to the scientific community. Although analysing this data is promising, the characterization of genes or genomes, on the other hand, is progressing very slowly and remains a major challenge for scientists. The aim of this study was to use GWAS approaches to decipher genomic loci without a priori assumptions. The microalga Tisochrysis lutea was selected as a case study due to its economic importance and the extensive knowledge accumulated over the years. Particular attention was paid to pigment and lipid metabolism due to their high commercial value. To implement the GWAS approach, a collection of algal lineages was established (100 lineages) from available polyclonal strains (15 strains). This collection was then phenotyped under two different culture conditions. Of the 31 phenotypic traits investigated, 18 met the requirements for GWAS analysis. Concurrently, each algal lineage was genotyped by whole genome sequencing to inventory all genetic polymorphisms. A mixed model was applied, revealing 13 significant associations between phenotypic traits and alleles. These associations highlight previously unsuspected genomic loci that play a major role in pigment or lipid content. Genes identified at these loci may have a direct or indirect role in these metabolic pathways. Nevertheless, elucidating the molecular mechanisms of the associated genes remains limited without the implementation of functional approaches. Despite the complexity of the process, we conclude that the GWAS approach was effective for deciphering phytoplankton genomes, particularly for quantitative traits of interest. Ideally, this approach should be combined with other functional methods to progressively decode marine genomes.

Garra rufa, commonly known as the doctor fish, is a small freshwater cyprinid notable for its exceptional tolerance to high temperatures, surviving even at around the human body temperature of 37 {degrees}C, and has emerging potential as a novel laboratory model for human cancer xenotransplantation and infectious disease research. To establish a foundation for its experimental use, we conducted comprehensive anatomical and histological analyses across major organ systems. The overall body organization and tissue architecture of G. rufa are broadly similar to those of zebrafish (Danio rerio), indicating a conserved cyprinid body plan. However, several organ systems in G. rufa exhibited species-specific differences compared with zebrafish, including a well-developed adhesive disc around the oral region, a long and coiled intestine, and a distinct dark pigmentation of the peritoneum. These species-specific traits may reflect ecological and behavioral adaptations of G. rufa, including benthic scraping in warm, flowing habitats. Physiological assays confirmed that G. rufa maintains high survival rates and normal swimming activity at 37 {degrees}C, whereas zebrafish exhibit significant mortality and reduced locomotion under the same conditions. Collectively, this work provides a comprehensive histo-anatomical atlas of G. rufa, highlighting its unique morphological specializations while establishing an essential reference for the development of this species as a novel experimental fish model.

Astyanax Baird & Girard, 1854 is a widely distributed and species-rich genus of Acestrorhamphidae, whose abundant populations in Neotropical basins play a crucial ecological role at the trophic level. Taxonomic uncertainties persist within the genus, as seen in Astyanax sp. (formerly designated as A. fasciatus) from the Magdalena basin in Colombia. Concerns about its genetic status are heightened due to ecological threats posed by hydroelectric dams, from habitat loss to river connectivity. We isolated and characterized 17 microsatellite loci to assess the population genetics of this species in a broad sample from the middle and lower sections of the Cauca River, now interrupted by the Ituango dam. Furthermore, a multidisciplinary approach integrating phylogenetic analyses of mitochondrial (COI) and nuclear (rag2) markers with geometric morphometric analyses was employed to evaluate potential cryptic diversity within Astyanax sp. Microsatellites revealed two genetic groups in the studied area, strongly supported as distinct lineages by phylogenetic analyses. Unexpectedly, one of these lineages of Astyanax sp. was recovered in an unresolved clade with samples of A. microlepis and allopatric samples of A. viejita from the Maracaibo Lake basin. Each genetic group showed high genetic diversity, but also evidence of recent bottleneck events and significant-high values of inbreeding. Morphometric analyses provided evidence of significant phenotypic differentiation among A. microlepis, Astyanax sp. 1 (Asp1), and Astyanax sp. 2 (Asp2). Morphological patterns ranged from the robust profile of A. microlepis to the streamlined shape of Astyanax sp. 2 (Asp2), with Astyanax sp. 1 (Asp1) displaying intermediate traits and localized differences in head length and fin placement. Statistical support from permutation tests and a high overall classification accuracy (95.65%) underscore the existence of distinct morphospecies, suggesting that phenotypic differentiation is well-established, despite the complex evolutionary history of the group. This study suggests the presence of cryptic diversity within Astyanax sp. and provides valuable genetic information for the conservation and management of their populations in the Magdalena basin.

Spanish clam fisheries have contracted sharply over the past two decades, with repeated closures and declining landings affecting coastal livelihoods. Using local ecological knowledge (LEK), we examine how fishers, fishers guild leaders and regional managers interpret (i) ecological change and (ii) the institutional conditions shaping management outcomes in Spains main clam fisheries, focusing on wedge clam (Donax trunculus), striped venus clam (Chamelea gallina) and smooth clam (Callista chione). We conducted 94 semi-structured interviews (April 2024-August 2025) across the Spanish Mediterranean and the south Atlantic coast (Catalonia, Valencian Community, Balearic Islands, Murcia and Andalusia). Stakeholders characterised declines as a cumulative process driven by interacting stressors: climate variability and extremes, coastal habitat alteration, pollution, episodic disease events and fishing pressure intensified by illegal extraction and informal marketing. Governance assessments were predominantly negative, emphasising fragmented authority across administrative scales, delayed or reactive measures, uneven rules among gears exploiting shared stocks, limited user influence in decision-making, and chronic monitoring and enforcement gaps, especially for shore-based fisheries operating outside port-based control points. Overall, LEK closely aligns with scientific evidence on cumulative stressors, suggesting that persistent declines reflect less a lack of ecological understanding than institutional constraints that hinder timely, legitimate and enforceable responses. Policy priorities include climate-adaptive harvest rules linked to environmental indicators, co-produced monitoring, strengthened traceability and compliance, harmonised rules across gears and management units, and improved cross-sector coordination to reduce conflict and safeguard nearshore habitats. HighlightsO_LIStakeholders across Spain describe clam declines as the outcome of interacting ecological, climatic, and governance stressors rather than as the consequence of isolated drivers. C_LIO_LIPerceived drivers differ regionally: climate- and habitat-related pressures dominate the Mediterranean, while effort, illegal fishing, and market dynamics are more salient in the Gulf of Cadiz. C_LIO_LIMost interviewees view management and governance as ineffective, citing fragmented authority, uneven rules among gears and regions, and weak enforcement. C_LIO_LIInformal practices (off-auction sales and poaching) are repeatedly identified as mechanisms undermining legitimacy, traceability, and effort controls--particularly in nearshore wedge clam fisheries. C_LIO_LIPolicy pathways include harmonising cross-scale rules, strengthening monitoring and compliance, and institutionalising co-management that integrates LEK with science. C_LI