Journal of Fish Biology

A new species of eight‐gilled hagfish genus Eptatretus (Myxinidae) is described based on five specimens trawled on the upper continental slope off Kollam, Kerala, India, northern Indian Ocean. Eptatretus gopali sp. nov. can be diagnosed by the presence of eight‐gill pouches and gill apertures, 10–11 pre‐brachial, 7 branchial, 50–55 trunk, 9–10 tail slime pores, 77–82 total pores, 3/2 multicusp teeth pattern, 40–44 total cusps, absence of nasal‐sinus papillae, and a light brown body color. Detailed morphological comparisons with all known eight‐gilled species of Eptatretus showed that the new species was distinct from all others by having 40–44 total cusps, characteristic body proportions, and the shortest tail length. E. gopali formed a district clade in the phylogenetic tree and exhibited a genetic distance of 3.6%–11.6% in Cytochrome C oxidase I (COI) sequences and 2.0%–4.9% in 16S rRNA sequences between the congeners. An identification key is also provided for the species of Eptatretus from the Indian Ocean.

Animal growth is a fundamental component of population dynamics, which is closely tied to mortality, fecundity, and maturation. As a result, estimating growth often serves as the basis of population assessments. In fish, analysing growth typically involves fitting a growth model to age‐at‐length data derived from counting growth rings in calcified structures. Additionally, fish growth can be estimated using length‐frequency data or data on changes in length derived from mark‐recapture events. In our study of the European grayling (Thymallus thymallus L.) in the alpine region of Germany, we utilized all three types of datasets to develop the initial growth model. For the age‐at‐length data from scales, we applied the traditional von Bertalanffy growth function using both a Bayesian and a frequentist approach. Furthermore, we adopted the mark‐recapture data along with the Fabens model for reparametrizing the von Bertalanffy growth model. The electronic length‐frequency analysis (ELEFAN) was employed to examine the length‐frequency data of the grayling, encompassing multiple sampling events from 2013 to 2022. Our findings indicated that the mark‐recapture data, in conjunction with the Fabens model, yielded the most plausible values for both statistical approaches. When the von Bertalanffy growth function was used, the frequentist approach generated unreasonably high values, whereas the Bayesian version produced meaningful results when appropriate priors were applied, suggesting potential issues with the age‐at‐length data related to ageing. The ELEFAN approach produced the smallest yet reasonable growth parameters, contradicting other studies on the European grayling. The lower values may be attributed to the lack of larger fish in most of the sampling events, resulting in a relatively low asymptotic length and slow growth rate. As demonstrated in this case study on grayling from the River Inn, the use of growth characteristics may be a currently underestimated yet very useful indicator of target species assessment that can nicely complement other population health indicators.

The diet of indicator fish species plays a crucial role in assessing ecosystem health. This study evaluated streams with and without urban influences, focusing on abiotic parameters and the trophic ecology of Psalidodon fasciatus and Piabina argentea. Forested streams exhibited higher redox potential, dissolved oxygen, transparency, and depth, whereas urban streams had higher temperatures, greater widths, and increased levels of total dissolved solids, conductivity, total coliforms, and thermotolerant coliforms. The P. fasciatus population exhibited isometric growth in forested streams and negative allometric growth in urban streams. Conversely, P. argentea exhibited negative allometric growth in both types of environment. The diets of both species included items of autochthonous and allochthonous origin. P. fasciatus had a similar diet in both stream types, whereas P. argentea's diet varied significantly between forested and urban streams. These findings highlight the importance of understanding the interplay between environmental characteristics and species diets, offering crucial insights into the health status of streams, especially those impacted by urbanization.

The tambaqui (Colossoma macropomum, G. Cuvier 1818) thrives both in the ion‐poor waters of the Amazon and in commercial aquaculture. In both, environmental conditions can be harsh due to low ion levels, occasional high salt challenges (in aquaculture), low pH, extreme PO2 levels (hypoxia and hyperoxia), high PCO2 levels (hypercapnia), high ammonia levels (in aquaculture), and high and low temperatures. Ion transport across the gill is affected by active transport processes, passive diffusive permeability, ion concentrations (the chemical gradient), and transepithelial potential (TEP, the electrical gradient). The latter is a very important indicator of ionoregulatory status but is rarely measured. Using normoxic, normocapnic, ion‐poor, low–dissolved organic carbon (DOC) well water (27°C, pH 7.0) as the acclimation and reference condition, we first confirmed that the strongly negative TEP (−22.3 mV inside relative to the external water) is a simple diffusion potential. We then evaluated the effects on TEP of more complex waters from the Rio Negro (strong hyperpolarization) and Rio Solimões (no significant change). Additionally, we have quantified significant effects of acute, realistic changes in environmental conditions—low pH (depolarization), hypercapnia (depolarization), hypoxia (depolarization), hyperoxia (hyperpolarization), elevated NaCl concentrations (depolarization), and elevated NH4Cl concentrations (depolarization). The TEP responses help explain many of the changes in net Na⁺ flux rates reported in the literature. We have also shown marked effects of temperature on TEP and unidirectional Na⁺ flux rates (hyperpolarization and decreased fluxes at 21°C, depolarization and increased fluxes at 33°C) with no changes in net Na⁺ flux rates. Calculations based on the Nernst equation demonstrate the importance of the TEP changes in maintaining net Na⁺ balance.

Anadromous salmonids migrate seaward to exploit feeding and growth opportunities in marine habitats, yet how smolt biological characteristics influence their marine migratory behavior remains poorly understood. This study used 9 years of trout (Salmo trutta) population monitoring data from 15,595 tagged age‐0+ parr, 1033 smolts detected migrating downstream in spring, and 99 adults detected returning from their first marine migration to the River Frome (Dorset, UK) to investigate the influence of smolt biological characteristics on their migration timing and maiden marine sojourn duration. Age‐specific differences in the influence of smolt length on migration timing were found, with longer 1‐year‐old smolts emigrating later than their shorter counterparts within the same age class, but the opposite association existed for 2‐year‐old smolts. A bespoke integrated statistical model quantified the effects of smolt emigration day of year, age, sex, and length on the probability of first‐time migrants returning to the river after one or more sea winters. Younger, later migrating smolts had a longer marine sojourn duration than their older, earlier migrating counterparts, and females remained at sea for longer periods than males. Although the statistical model was designed to maximize the use of information available in the data, it revealed only weak effects of smolt biological characteristics on the maiden marine sojourn duration. A complementary simulation study suggested that detecting more spring migrating smolts and analyzing longer time series of trout population monitoring data would increase the ability to detect statistically significant effects. Therefore, a strategic review of the trout population monitoring program, including more long‐term biological data collection, is recommended. The modelling work presented here can provide guidance on the size of the required dataset and how to maximize the power of imperfect data.

The deep‐sea demersal fish fauna is characterized by a prevalence of elongated‐body forms with long tapering tails. Using baited camera landers at depths of 4500–6300 m in the Pacific Ocean, we observed multiple instances of backward swimming using reverse undulation of the slender body in four species: the cutthroat eel Ilyophis robinsae, abyssal grenadier Coryphaenoides yaquinae, and cusk‐eels Bassozetus sp. and Barathrites iris. Backward swimming was used as an escape or repositioning maneuver, reversing for up to seven tail beats before resuming forward swimming in a new direction. The eel I. robinsae reversed with a swimming wave frequency of 0.51–0.95 Hz, wavelength 0.6–0.75 of the body length (L), and large amplitude movements of the head from side to side. C. yaquinae reversed relatively slowly at 0.21–0.52 Hz and wavelength 0.5–0.7 L aided by propulsive movements of the pectoral fins and minimal lateral movement of the head. The ophidiids also used reversed propulsive body waves augmented by paddling with the pectoral fins but with some lateral movement of the head. Pectoral‐fin movements in all species were in synchrony with the body movements. The elongated‐body form enables backward swimming by reversal of the anguilliform propulsive wave and has the advantage that the fish automatically returns to safety along the path recently traveled. This maneuverability conferred by an elongated body may be a significant factor in selection for body shape in deep‐sea fishes.

Pacific Island communities are heavily dependent on fisheries for subsistence and livelihoods. Yet, despite their importance, coastal fisheries are poorly managed and commercial pressures increasingly threaten them. Groupers (Epinephelidae) are exceptionally vulnerable to overexploitation due to aspects of their biology while their economic value makes them a prime target for commerce. Fiji has a significant grouper fishery and is a useful case study to assess a data‐poor, economically valuable sector to evaluate management measures, options, and needs. Data from multiple sources over three decades were integrated with original research involving fisher interviews, market surveys, stock assessments, and underwater census to assess the status of the country's grouper fishery. Catch rates are declining and trade now includes a high percentage of immature groupers, with aggregating species (mainly Epinephelus polyphekadion, Epinephelus fuscoguttatus, Plectropomus areolatus, Plectropomus leopardus) particularly at risk. Estimated annual grouper landings are increasing and now exceed 1000 mt. There is an urgent need to update Fiji's grouper size limits which are grossly inadequate. To build public support and increase awareness, government and nongovernmental organizations should invest in the national 4FJ Fish Smart campaign. Key management recommendations for groupers are (1) improved spatial and temporal protection of spawning aggregations and (2) increased minimum‐size restrictions for capture and sale. Findings apply broadly to valuable and vulnerable coastal fin‐fisheries in reef ecosystems across many Pacific Island countries and highlight the importance of using multiple data sources and approaches to understand and manage important data‐poor fisheries.

Understanding the developmental sequence characteristics of the vertebral and appendicular skeletons of the larvae and juveniles of Larimichthys crocea (Naozhou population) can provide theoretical basis for seedling cultivation, environmental adaptation, and taxonomic identification. The cartilage‐bone double staining method was used to stain, observe, and analyse the vertebrae, pectoral fins, anal fins, caudal fins, and dorsal fins of the larvae and juveniles of L. crocea (0–30 days post‐hatching [DPH]). Results showed that the notochord of the larvae and juveniles of L. crocea was tubular. At 6 DPH, there was obvious segmentation. At 8 DPH, the neural arches began to differentiate, and at 10 DPH, the haemal arches began to differentiate, with complete segmentation of the notochord. At 14 DPH, the dorsal and ventral ribs became clear, and the neural and haemal spines were completely formed by the elongation of the neural and haemal arches, respectively. At 18 DPH, the vertebral bones began to ossify, and ossification was complete at 28 DPH. The median fins of the larvae and juveniles of L. crocea formed in the order of caudal fin, anal fin, and dorsal fin. Among the 800 L. crocea larvae samples, 248 were observed to have skeletal deformities, with a deformity rate of 31.00%. The spine of L. crocea consists of 26 vertebrae, with developmental abnormalities mainly including vertebral anterior convexity, bifurcation of neural spines, vertebral body fusion, and redundancy of neural spines. The above results provide a theoretical basis for enriching the developmental biology of L. crocea.

Preference tests are commonly used to assess fish behavior and cognition in several research fields. This study aimed to investigate how fish perform in a preference test involving extended habituation to the apparatus, which was expected to reduce stress. We contrasted the choice between a sector of the apparatus with natural vegetation, expected to be the preferred stimulus, and a barren sector. Initially, we demonstrated that guppies' preference for the sector with vegetation increased after a 5‐day habituation period (Experiment 1). Subsequent experiments systematically modified the testing paradigm to observe effects on the preference. Experiment 2 introduced a physical separation between sectors to facilitate discrete choices, Experiment 3 tested groups of fish, and Experiment 4 used wild guppies. Only the modification in Experiment 3 impacted preference scores: guppies tested in groups showed a higher preference for the vegetation stimulus and spent less time in the central, no‐choice sector of the testing apparatus. Overall, this study supports the importance of methodological details in preference tests and highlights the benefits of extended habituation and group testing. Researchers should consider these factors when designing experiments to evaluate cognitive abilities or behavioral preferences in fish. Tailoring testing paradigms to specific research goals can improve the reliability and comparability of results, contributing to a deeper understanding of fish behavior and welfare.

This study investigates the growth and calcification of the appendicular skeleton in Raja asterias (Delaroche, 1809), a member of the Batoidea, to explore the relationship between histomorphology and the mechanics of batoid locomotion within the water column. Although much prior research has focused on the “tessellated pattern” in these fishes, the variable structure of the appendicular skeleton provides fresh insights into the understudied interplay between skeletal histomorphology and the mechanical functions of Batoidea fins. The shape and initial growth of fin cartilage are influenced by the orientation of chondrocyte mitoses prior to mineral deposition, with subsequent calcification playing a pivotal role in shaping skeletal architecture. This study documents two distinct growth patterns: “crustal” and “catenated.” The crustal pattern is predominantly observed in larger skeletal elements, such as the central body structures (skull, rostrum, and jaws), girdles, pterygia, and compound radials, whereas fin radials follow the catenated growth pattern. Notably, early‐stage chondrichthyan cartilage shares similarities with mammalian metaphyseal growth plate cartilage, though in chondrichthyans, the calcified matrix is not resorbed or replaced by bone. Additionally, a previously unrecognized calcification pattern is identified in the pelvic‐fin radials of R. asterias, indicating that the mechanical demands of locomotion in the water column may have driven the evolution of variable fin flexibility in Batoidea. This flexibility is achieved through joint mobility (diarthroses and amphiarthroses), specialized fin structures, and the distinct calcification patterns of the pectoral and pelvic fins.

This study examined the effect of dietary selenium (Se) fortification on growth efficiency, antioxidant status, and liver gene expression in juvenile pangasius catfish. Sodium selenite was incorporated into a basal diet at incremental levels of 0–2.0 mg Se/kg. This resulted in final Se concentrations of 0.63, 0.85, 1.15, 1.68, 2.10, and 2.65 mg Se/kg, respectively. A total of 15 fish, with an average individual weight of 5.6 ± 0.1 g, were subjected to one of six dietary treatments and fed in triplicate over a 60‐day period. A significant dose‐related enhancement in growth performance was observed, with the optimal dietary Se requirement estimated at 1.75 mg Se/kg. Se‐fortified diet significantly increased the activities of digestive enzymes (lipase and protease) as well as antioxidant enzymes, including catalase, glutathione peroxidase, and superoxide dismutase in the liver. Notably, the group fed 1.68 mg Se/kg displayed the highest levels of these enzymes. Additionally, selenium supplementation resulted in an upregulation of the relative expression of insulin‐like growth factor 1X1 and 1X2 in the liver, highlighting its pivotal role in growth regulation. Blood parameters showed significant improvements in mean corpuscular hemoglobin and hemoglobin levels with Se supplementation. Proximate analysis showed increasing Se intake resulted in a significant rise in muscle protein content. In pangasius catfish, our results indicate that dietary selenium supplementation can enhance growth efficiency, antioxidant capacity, and hepatic gene expression.

The roundscale spearfish (Tetrapturus georgii) is a poorly studied species with limited information available on its biology, ecology, and population status. Although the adult life stage of the species is morphologically distinguishable from closely related species such as the overexploited white marlin (Kajikia albida), misidentification is common, adding to the uncertainties connected with population assessments of these pelagic highly migratory species. Although genetic studies have recently confirmed its distinction from congeneric species, much of the reproductive biology and population dynamics of T. georgii remain unknown, underscoring the need for further research to guide conservation and management strategies. This study reports the first documented records of an egg and a juvenile T. georgii. Here, we provide photographs, morphological descriptions, and collection site data for genetically confirmed egg and juvenile specimens obtained during two multipurpose research surveys in the Sargasso Sea Subtropical Convergence Zone. These findings contribute new insights into the reproductive biology, early life stages, and ecology of this elusive species.

The lamprologine cichlid genus Telmatochromis was long considered primarily lacustrine and endemic to Lake Tanganyika until an undescribed Telmatochromis species was reported from the Lufubu River (Lake Tanganyika drainage, Zambia). A phylogenomic study in 2021 confirmed the association of Telmatochromis sp. “lufubu” with Telmatochromis along with another riverine species, Neolamprologus devosi (Malagarasi drainage, Tanzania). Here, we quantify the morphological diversity of the genus Telmatochromis and the two associated riverine species using a multivariate dataset combining geometric and classical morphometrics, as well as meristics. We identify three distinct morphological clusters: the “Telmatochromis vittatus complex” with highly elongated bodies and short heads, the “Telmatochromis temporalis complex” with deeper bodies, and the two riverine species with intermediate body elongation and large heads. Further, we formally describe the species endemic to the lower Lufubu River as Telmatochromis salzburgeri sp. nov. and reassign N. devosi to Telmatochromis. Telmatochromis devosi comb. nov. differs from all congeners by the absence of bi‐ and tricuspid teeth in the inner tooth rows of the oral dentition. T. salzburgeri sp. nov. can be distinguished from all other Telmatochromis species by a prominent orange stripe along the base of the dorsal fin and from T. devosi comb. nov. by the relatively smaller size of the lower pharyngeal jaw. Both riverine species differ from all lacustrine Telmatochromis by a lower number of dorsal‐fin spines. Additionally, the riverine species can be distinguished from the T. vittatus complex by having larger heads and longer oral jaws, and from the T. temporalis complex by their lower relative body depth. With the inclusion of new riverine members, the genus Telmatochromis is revealed to be more morphologically and ecologically diverse than previously recognized.

With the expanding global population, interest has increased in the sustainable aquaculture development of indigenous fishes. In Hawaiʻi, the brassy chub, Kyphosus vaigiensis, has drawn interest as a candidate species for production. However, little is known about its resilience in aquaculture settings where fish are exposed to acute, husbandry‐related stressors. To address the response of brassy chub to handling stress, we characterized the effects of simulated netting and confinement stress on physiological parameters indicative of the alarm and resistance phases of the stress response over a 24‐h time course. Specifically, we measured plasma osmolality and glucose, mucous cortisol, hepatic activity of the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX), and hepatic lipid peroxidation (LPO). Plasma osmolality in stressed fish was increased relative to controls at 1 and 6 h. Mucous cortisol levels were transiently increased in stressed fish at 1 h following handling stress. In stressed fish, plasma glucose was generally increased from 1 h to 24 h relative to controls. By contrast, SOD activity decreased in stressed fish at 6 and 12 h, returning to control levels at 24 h; GPX activity and LPO were unaffected by the handling stressor. The transient and modest responses of mucous cortisol and antioxidant enzyme activity indicate the recovery of brassy chub from handling stress. Moreover, the sustained increase in plasma glucose and lack of change in LPO suggest mobilization of energy and long‐term resiliency toward handling stressors.

Due to the logistical and financial challenges in studying migratory marine species, there is relatively limited knowledge of the reproductive biology, behavior, and habitat use of many ecologically important marine megafauna species, including the Atlantic tarpon Megalops atlanticus. Here, we present a novel observation using consumer‐grade aerial drones to observe, quantify the scale of, and classify behaviors within a previously unreported tarpon aggregation (N = 182) over the course of a 2‐day fish aggregation event. After the event, we analysed and compared observed behaviors (e.g., cruising and clustering) with those of other fish species with well‐documented reproductive behaviors, revealing behaviors potentially consistent with courtship, leading us to believe this to be a possible spawning aggregation or aggregation of reproductive/migratory significance. This aggregation occurred in highly altered and urbanized habitat off the coast of South Florida, during the winter, and outside of tarpon's previously reported spring and summer spawning season. Although few studies to date have used drones to monitor teleosts, this study reinforces their potential value as a tool for monitoring fish populations, behavior, and movement.

The spurdog (Squalus acanthias Linnaeus, 1758) is a globally distributed squaliform shark that has historically been overfished but is now recovering in the northeast Atlantic. Data series on spurdog movement and habitat use have been somewhat limited to research surveys due to challenges associated with electronic tagging. Here, we offer a revised attachment method for externally attached pop‐up satellite archival tags that was successful in long‐term deployments on pregnant females. Twenty‐one spurdogs were tagged in two fjord systems in western Norway for an average of 243 days and provided new details about their behaviour, demonstrating affinity for coastal habitat based on the pop‐up locations and recovery positions of the tags (84% within 40 km from tagging location), and depth–temperature profiles. It is likely that parturition therefore occurs in these coastal waters, making them important to the life cycle of this species. The realized depth niche of tagged individuals suggested that surveys may miss sharks if they do not cover the full water column because the sharks used large parts of the water column and spent much time in shallower waters, albeit with seasonal variations (deeper and shallower in winter and summer, respectively). Adoption of this tagging method and combination with movement data from acoustic transmitters will help to better resolve the behaviour of this species as it transitions from a species at risk to a managed fishery. Such studies will provide a more comprehensive understanding of the species' habitat requirements that will empower better informed protections against a return to the red list of threatened species.

Fish presence in tailraces is a remarkable management concern in operating hydroelectric power plants (HPP) in Brazilian rivers. Fish get blocked during upstream migration for spawning, and large shoals can last for days in the tailrace; however, the circumstances that attract fish throughout the year to this region are uncertain, especially during drought conditions. To unravel this uncertainty, we modeled the relationship between Pimelodus maculatus abundance and environmental and operational variables (N = 26) in monthly fishing campaigns at the Machadinho HPP (N = 18). A generalized additive model was fitted to fish abundance in which water conductivity, 30‐day accumulated precipitation, reservoir inflow, and seasonality explained 93% of the deviance. It was found that abundance decreased as water conductivity increased, but abundance was higher in summer. However, winter showed the highest abundance in the entire rainfall range with peaks between 130 and 150 mm and above 250 mm. An increase in reservoir inflow decreased fish abundance. During droughts, our findings suggest that the powerhouse foundations, particularly the draft tube, may serve as refugia to P. maculatus.

This study investigated the effects of pre‐experimental fasting for 2, 7, and 14 days under both unsheltered (12 h dark–12 h light) and sheltered conditions on the critical swimming speed (Ucrit) and oxygen consumption (MO2) of juvenile grass carp, using a modified swim respirometer. Key findings include (1) the Ucrit of test fish decreased significantly, by 28%, after fasting for 14 days and sheltering intensified the impact to a 43% decrease, and (2) fish anaerobic capacity decreased after 7 days but increased after 14 days, and was enhanced by sheltering conditions. These findings are important as they indicate that fasting and sheltering can impair grass carp survival and disrupt river ecosystem balance, highlighting the need for habitat conservation.

The Atlantic wolffish (Anarhichas lupus) is a cold‐water fish with potential for aquaculture diversification. To unveil the mechanisms underlying the compromised growth in Atlantic wolffish when reared at higher temperatures, we investigated the relationship between temperature, growth rate, aerobic capacity, stress biomarkers, and gut barrier function. Juveniles acclimated to 10°C were maintained at 10°C (control) or exposed to 15°C for either 24 h (acute exposure) or 50 days (chronic exposure). Fish exposed to 15°C exhibited reduced growth, higher standard, and maximum metabolic rates compared to those at 10°C. In the chronically exposed group at 15°C, metabolic rates were lower than those of acutely exposed fish. The absolute aerobic scope exhibited no significant variation in temperatures; however, the factorial scope showed a notable reduction at 15°C in both acute and chronic exposed groups, aligning with a correlated decrease in individual growth rates. Chronic warming led to increased plasma glucose levels, indicating energy mobilization, but cortisol levels were unaffected. Furthermore, chronic warming resulted in reduced intestinal barrier function, as evidenced by increased ion permeability and a negative potential in the serosa layer. We conclude that warming elevates metabolic rates while reducing intestinal barrier function, thus increasing energy expenditure, collectively, limiting energy available for growth at this temperature from increased allostatic load. Thus, juvenile wolffish maintaining their aerobic scope under thermal stress experience slower growth. This research provides insights for improving the welfare and resilience of wolffish in aquaculture at elevated temperatures and understanding their response to increased environmental temperatures.

Fish visceral waste, which is normally discarded, is considered one of the richest sources of proteinases with potential biotechnological applications. For this reason, alkaline proteinases from viscera of Argentine hake Merluccius hubbsi, Brazilian flathead Percophis brasiliensis, Brazilian codling Urophycis brasiliensis, and stripped weakfish Cynoscion guatucupa were characterized. Individuals were caught by a commercial fleet off the coast of the Argentinean Sea. The intestine and pyloric caeca were dissected out and then minced and triturated with distilled water. The proteinase activity of P. brasiliensis extracts was enhanced by all the ions tested (Mn²⁺, K⁺, Na⁺, Ca⁺²) while the enzymes of the other species were stable in the presence of those ions, retaining more than 60% of their enzymatic activity. Alkaline proteinases of all species showed extreme stability to 5% v/v surfactants at 60 min (Sodium dodecyl sulfate, Triton X‐100, Tween 20, Tween 80), and relative stability toward an 6% v/v oxidizing agent (H2O2) and organic solvents 80% (acetone, isopropanol, methanol, ethanol). The enzyme extracts were incubated for 60 min with these compounds. Interestingly, alkaline proteinases from all species were compatible with the commercial detergents (Ala, Skip, and Ace). These results demonstrate that proteinases recovered from a no‐cost sample such as fishery residues can be used for industrial applications, such as detergent formulations.

The study investigated the potential alleviating effect of sodium butyrate (SB) on intestinal injuries caused by glycinin in the diet of common carp. Fish were divided into six groups: a control group (without glycinin and SB), a Gly group (with glycinin), and four groups supplemented with different doses of SB (0.75, 1.50, 2.25, and 3.00 g/kg) based on the Gly group. All diets were isonitrogenous and isoenergetic, and the fish were fed these diets for 8 weeks. The results indicated that glycinin activated the mitogen‐activated protein kinase (MAPK) signaling pathway, leading to upregulating ERK, JNK, and p38 gene expression in the intestine. However, SB2 and SB3 groups were able to inhibit this pathway. Furthermore, glycinin upregulated the expression of proapoptotic genes (Bax, Caspase‐3, Caspase‐8, and Caspase‐9) while downregulating the antiapoptotic gene Bcl2. The SB2 and SB3 groups were found to alleviate glycinin‐induced apoptosis. Additionally, dietary glycinin significantly decreased the expression of tight junction genes (ZO‐1, Claudin3, Claudin7, and Occludin1) in the intestine, whereas the SB2 and SB3 groups improved intestinal barrier function. Glycinin also elevated serum levels of d‐lactate, diamine oxidase, serotonin, and endothelin, resulting in intestinal damage and increased permeability. In contrast, the SB2 and SB3 groups reduced these serum levels, thereby regulating intestinal permeability. Moreover, glycinin disrupted the intestinal morphology, which was mitigated by the SB2 and SB3 groups by increasing the height and width of intestinal villi folds. Lastly, dietary glycinin altered the intestinal microecological balance by increasing Proteobacteria abundance and decreasing Clostridium and Bacteroidetes abundance. The SB2 and SB3 groups modulated the composition of dominant taxa by increasing Firmicutes and Acidobacteria abundance. Overall, SB was found to mediate the MAPK signaling pathway, apoptosis, upregulation of tight junction genes, maintenance of the intestinal physical barrier, and regulation of intestinal flora, thereby alleviating glycinin‐induced intestinal damage.

The diamond stingray (Hypanus dipterurus) is a species of cartilaginous fish that, according to the IUCN, is globally in a vulnerable state of conservation and its populations show a decline. New records of this ray species in southern Peru and northern Chile have expanded their known range. The species is distributed in the Eastern Central Pacific, from southern California to San Andres, on the central coast of Peru, but is poorly known in Chile. Angler records mined from social media and historical data confirmed the presence of H. dipterurus along southern Peru and northern Chile, extending southward over 1250 km. A species distribution model (SDM) based on previous global occurrences combined with oceanographic layers was built to identify areas of potential and undocumented presence of H. dipterurus. The SDM showed high accuracy (area under the curve = 0.95) and predicted the potential presence of H. dipterurus along vast areas of the Peruvian and Chilean coasts, where the presence of the species was poorly documented. Comprehensive surveys are required to understand the distribution, population dynamics, habitat requirements, and threats to effective conservation efforts in the southern region of its distribution range.

A workflow for developing a cost‐ and time‐efficient, single nucleotide polymorphism (SNP)‐based assay for species and hybrid identification is described. In a reference set (n = 46), the developed assay identified individuals of two closely related species, the Atlantic salmon (Salmo salar L., n = 23) and brown trout (Salmo trutta, n = 23), with 100% accuracy. Furthermore, species and hybrid identification using field‐collected embryos had 98.1% concordance (155/158) to more expensive and time‐consuming methods that utilized multiple SNP markers. The method can be integrated into management and conservation plans to quantify species' spawning distribution and hybridization rates.

Active (i.e., intentional) fish sound production provides informative cues for numerous ecological functions, including larval recruitment or reproduction, and can facilitate monitoring and restoration. It is therefore important to have a holistic picture of actively soniferous tropical reef fish diversity, particularly in the face of growing threats such as noise pollution and habitat degradation. This study integrates fish biodiversity and sonifery datasets to assess the prevalence and ecological characteristics of actively soniferous tropical reef fishes. There are 258 known sound‐producing species, which span 46 families, encompass a variety of life‐history (e.g., lifespan) and distribution (e.g., depth) attributes, and include many vulnerable and commercially valuable species. Furthermore, up to 75% of tropical reef fish species are considered likely to produce active sounds. This synthesis should encourage a greater appreciation for active fish sound production in tropical reef environments and advance efforts to incorporate soundscape ecology into management and restoration strategies.