Fishes, Volume 10, Issue 1 (January 2025) – 36 articles

Freshwater fish community surveys are an important component of aquatic ecosystem management. However, the standard method for taxonomic identification currently used for these surveys, wherein fishes are manually identified in the field by a taxonomic expert, has several shortcomings. These include handling-related fish injury and mortality, the need for a fish-identification expert to be present during field sampling, and additional fish mortality due to physical voucher collection. These shortcomings may be overcome using new methods such as environmental DNA (eDNA) or image analyses. While eDNA can provide fish community data through metabarcoding, it is costly and provides little ecological information. A novel, image-based method for taxonomic identification (“batch-image identification”), which addresses the shortcomings of standard and eDNA methods, was tested in this study. Fishes were captured in the field and photographed in small groups (“batches”) within fish viewers for subsequent identification by taxonomic experts. Comparing taxonomist-based identifications from batch images to specimen-based identification, batch-image identification yielded an overall species-level correct-identification rate (CIR) of 49.7%, and an overall genus-level CIR of 61.2%. CIR increased with taxonomist expertise, reaching 83% when identification was performed by expert taxonomists. Batch-image identification data also produced rarefaction curves and fish-length measurements comparable to those obtained through standard methods. Potential methodological improvements to batch-image identification, including procedural adjustments and alternative identification methods, provide direction for the continued testing and improvement of this method. Full article

Walleye pollock (Gadus chalcogrammus) is a commercially important species widely distributed in cold-water regions. We have been culturing this species artificially since 2015. The average embryo diameter was 1.43 ± 0.056 mm, and hatching occurred at 5 °C approximately 339 h post-fertilization. Gonadal development became visibly apparent at a body size of 10–15 cm after ~180 days, initially distinguishing ovaries with the development of germ cells, whereas testes were observable after further maturation. We discovered two intersexes from F1 and F2 generations, and one abnormal mature individual from F2. Morphologically, intersex walleye pollock exhibited distinct characteristics of ovary and testes, with male gonads visibly connected to the end of ovaries. In intersex walleye pollock aged 3–6 years, the gonads developed normally, and oocyte resorption was restricted to the area near the connections between testicular and ovarian tissues, with numerous atretic oocytes observed in the resorption zone. Primordial germ cells were found together in individuals who had not undergone spawning, indicating an abnormal maturation pattern. Although no significant differences in the gonadosomatic index were observed between intersex and normal individuals, further research on intersexuality is necessary to understand the reproductive development of this species and the health of offspring spawned by intersex individuals, which are rare. Full article

The present study evaluates garlic powder (GP) effects on growth performance, feed utilization, gill parasitic treatment, and monogenean diversity. Thus, a trial was performed under controlled conditions with 84 juvenile Nile tilapia, Oreochromis niloticus (39.8 ± 8.8 g initial weight), from culture ponds with monogenean parasite presence for 30 days. Four balanced diets in protein (32.5%) and lipids (6.4%) with GP inclusion levels of 0%, 1%, 2%, and 3% were formulated, manufactured, and supplied daily at approximately 6.5% body weight/tank. The GP diets, compared to the Control (without GP), indicated that the three inclusion levels did not affect the water quality, survival, growth performance, and feed utilization parameters (p > 0.05). No differences were observed in the parasitological index of prevalence (20–25%), mean intensity (9.6–28), and mean abundance (2.7–5.3) among the experimental diets (p > 0.05), evidencing no effect by inclusion level. Efficacy among GP diets indicated a potential decrease in parasite number (13.4–45.6%) but not all monogenean gill parasites. In conclusion, GP diets did not affect the Nile tilapia survival, growth performance, and feed utilization parameters; therefore, its use is suggested as a preventive alternative for monogenean gill parasites. Full article

Chinese herbal medicines have become a new green feed additive in the aquaculture industry. The aim of this study is to investigate the effects of traditional Chinese herbal medicines (Isatidis radix, Forsythia suspensa, and Schisandra chinensis) on the growth performance, antioxidant capacity, and intestinal microbiota of hybrid snakehead (Channa maculata ♀ × Channa argus ♂). A total of 600 fish (mean weight: 15.85 ± 0.15 g) were randomly assigned to five groups, including the control group (CG), I. radix extract group (IRE), F. suspensa extract group (FSE), S. chinensis extract group (SCE), and the Chinese herbal medicine mixture group (CHMM; a mixture of extracts of I. radix, F. suspensa, and S. chinensis at the ratio of 1:1:1) for 6 weeks. The results show that the IRE-supplemented diet improved the survival rate (SR), feed efficiency ratio (FE), and condition factor (CF) compared to others. Compared to the control group, the activity of superoxide dismutase (SOD) in plasma and intestine was significantly increased in the FSE and CHMM groups, whereas the content of malondialdehyde (MDA) in plasma and liver was significantly reduced in the SCE group. A 16s rRNA analysis indicates that dietary supplementation with FSE significantly promoted the proliferation of Fusobacteriota, while IRE supplementation increased the alpha diversity of intestinal bacteria. In conclusion, the addition of I. radix to the diet of hybrid snakehead improves growth, antioxidant capacity, and liver and intestine health, and modulates the intestinal microbiota of snakehead positively. Full article

The Mediterranean aquaculture industry has recently been confronted with the appearance of a bile imprint on fish filets, which to-date remains of unknown etiology. This study investigates the involvement of common procedures applied before (fasting), during (confinement), and after (ice storage) fish harvesting. Two experiments were designed, one for gilthead seabream (Sparus aurata) and one for red seabream (Pagrus major). The fish were grouped according to fasting duration (1, 2, 3 days), harvesting method (stressed, unstressed), and ice storage (0 h, 48 h). In both species, the imprint appeared in all ice-stored fish for 48 h but not in fresh fish (0 h), the color of the imprint became darker as Days of Fasting increased, stressed fish had darker imprints than unstressed fish, and plasma and bile osmolality and cholesterol were significantly affected by treatments. The histological examination of the gallbladder in red seabream showed great variability in the muscularis thickness and appearance, regardless of treatment. These results are not conclusive as to the cause of the bile imprint appearance. However, they offer a first insight into an issue that bears significant impact in the marketing of aquaculture products and may foster further investigation in the search of the underlying causes of this reoccurring issue. Full article

Estuary perch (Percalates colonorum) are a long-lived and slow-growing species which are distributed throughout southeastern Australian estuaries. In Tasmania, only one known population remains which is located in the Arthur River, on the remote northwest coast. Tasmania is the only Australian state to list estuary perch as a wholly protected species (recreational and commercial), while other populations across their mainland distribution appear to be robust. A survey undertaken on estuary perch in the Arthur River in 2014–2015 indicated that the population was small (825–2375 fish) and dominated by three age classes between 12 and 14 years old. This population also has extremely low genetic diversity and is genetically distinct to mainland populations due to its geographic isolation. During a re-survey in December 2023, 378 estuary perch were captured, with 191 tagged and released, and 31 fish retained for age and gonad analysis. Although three strong age classes were detected (five, eight and twenty-three years), numerous weak and missing cohorts were apparent. This study also confirms this population has a delayed spawning season in comparison to mainland populations, with growth models and tag recaptures (32 fish) demonstrating a very slow but sexually dimorphic growth rate. By combining the datasets of the 2014/15 and 2023 survey, we present an updated understanding of the biology and population dynamics of this unique Tasmanian population, which has previously never been published. The results confirm the population is still reproductively active and stable; however, due to their restricted distribution, variable recruitment, slow growth, and small population, further conservation efforts are still required. Further legislative listings at both the state and federal levels are planned, which if successful will provide additional protection and assist in applications for external funding and resources. This will support the development of a recovery plan which will consider re-stocking efforts and re-establishment of previously inhabited waters and investigate potential actions to improve the genetics of the Tasmanian population. Additionally, educational campaigns to inform the public and recreational fishers on the status of estuary perch in Tasmania will be undertaken. Full article

Fishing vessels are known to have a fatality rate from accidents nearly 100 times higher than that of merchant ships. However, since most cases are resolved internally without maritime tribunals, obtaining accurate statistics on accidents is challenging, making quantitative analysis and evaluation of accident risks difficult. Studies using inconsistent analytical methods often fail to converge on unified results or preventive measures, which contributes to the persistently high occurrence of fishing vessel accidents. Therefore, this study aimed to establish a standardized method for analyzing marine accidents on fishing vessels by applying the Formal Safety Assessment (FSA) technique, originally developed for merchant ships. The research focuses on the globally prevalent trap boat fishery, specifically examining common injuries occurring on fishing vessels. Quantitative data were collected from insurance approval records, while qualitative data were obtained through surveys. The research followed the five stages of the FSA framework: hazard identification, risk estimation, identification of risk control options, cost-benefit assessment, and recommendations for decision-making. The findings suggest that the FSA framework can be effectively applied to analyze fishing vessel accidents based on insurance data, leading to selective and effective preventive measures. Full article

Aeromonas species are among the main pathogens causing rainbow trout infections. Silver nanoparticles (AgNPs) have a broad spectrum of antimicrobial properties and are usually produced by various green-synthesis methods. However, the application of commercialized AgNPs has not fully been clarified. Thus, the objective of this study was to evaluate the antibacterial activities of commercialized AgNPs (range of sizes 10–12 nm) on two contrasting A. salmonicida strains (I-1 and I-4), isolated from rainbow trout; the antibacterial mechanism, histopathological alterations and the expression of immune-related genes were investigated. In vitro, the minimal inhibitory concentration (MIC) was 10 µg/mL for I-1, and lowered to 9.5 µg/mL for I-4, respectively. AgNPs were shown to disrupt both the cell wall and membrane of I-1 and I-4, resulting in cell lysis and degradation. In vivo, rainbow trout challenged by immersed or intraperitoneally injected infection, the 10 µg/mL AgNP-treated groups, both showed delayed deaths and lower mortalities compared to the control groups, without any clinical signs and pathological changes. Especially for the virulent I-4, the enhanced expressions of immune-related genes TNF-α, IL-1β, IL-10 and IL-11 were significantly reduced in the AgNP-treated group, indicating a lesser inflammation due to the application of AgNPs. This study would lay theoretical foundation for the wide application of silver nanoparticles in fish diseases. Full article

Melatonin is a critical regulator of biological rhythms across organisms, transducing light signals into neuroendocrine signals that facilitate reproductive regulation in response to environmental cues. However, the precise mechanisms through which melatonin regulates reproduction in fish require further investigation. In this study, we employed molecular and organizational biological techniques to examine the expression patterns of melatonin and its five receptor subtypes (LcMTNR1A1, LcMTNR1A2, LcMTNR1B1, LcMTNR1B2, and LcMTNR1C) in various tissues of the large yellow croaker (Larimichthys crocea). Our results revealed significant expression of all receptors in the pituitary and testes, with distinct gender differences, including a lack of expression in the ovary. Moreover, our data indicate that melatonin and its receptors are primarily expressed during stage III, highlighting their role in sexual maturity. Enzyme- linked immunosorbent assay (ELISA) results further demonstrated that in vitro melatonin incubation in the brain of L. crocea influenced gonadotropin-releasing hormone (GnRH) and testosterone secretion in a dose-dependent manner, suggesting actions beyond the classical hypothalamic–pituitary–gonadal (HPG) axis. Overall, our findings provide new evidence supporting the role of the melatonin system in reproductive regulation in marine teleosts. Full article

The costly production of live microalgal feed prevents the inclusion of an extended nursery phase in bivalve aquaculture. One method of feeding juvenile bivalves that has received minimal attention is the use of dissolved nutrients to reduce the reliance on live microalgae as a sole feed input. This study aimed to determine whether dissolved sucrose could work as a supplement to live microalgae. Two different concentrations of dissolved sucrose (i.e., 100 μg mL⁻¹ and 1 mg mL⁻¹) were each provided daily for 2 h and 4 h to juvenile Greenshell^™ mussels as a supplement to a diet of live microalgae. The growth and survival of the mussels were measured over three weeks. All combinations of sucrose concentrations and exposures improved the growth of spat compared with the control without sucrose. However, the best-performing spat were provided with a concentration of 1 mg mL⁻¹ of dissolved sucrose for an exposure time of 4 h, which induced 57% greater spat growth daily compared with the control diet. The mussel spat supplemented with dissolved sucrose also accumulated greater carbohydrate content compared with those in the control treatment, indicating they were in greater nutritional condition. This demonstration that dissolved sucrose can significantly improve the growth and nutritional composition of mussel spat over periods as short as 2 h shows promise for the commercial application of sucrose as low-cost supplementary feed in bivalve nurseries. Full article

The aim of this study was to investigate the effects of dietary yeast polysaccharide (YPS) supplementation on the growth performance, whole-body composition, antioxidant capacity, and immunity of juvenile largemouth bass (Micropterus salmoides). In this study, five diets with YPS levels of 0.00% (control), 0.05% (0.05Y), 0.10% (0.10Y), 0.15% (0.15Y), and 0.20% (0.20Y) were designed and prepared. A total of 300 healthy fish (3.20 ± 0.03 g) were randomly divided into 15 floating cages (1 × 1 × 1 m) in five different groups, with three replicates per group, for an 8-week culture experiment. The 0.10Y and 0.20Y groups had significantly higher feed conversion ratios compared with the control group. There was no significant effect on any of the other growth indicators. Plasma biochemical indices showed that the 0.10Y group exhibited the highest plasma alkaline phosphatase content and the 0.20Y group exhibited the highest plasma glucose content. Plasma antioxidant indices (total antioxidant capacity, superoxide dismutase, and glutathione) and antioxidant genes (catalase and superoxide dismutase) were elevated in the 0.05Y or 0.10Y groups, and the malondialdehyde content decreased with increasing YPS concentration. Moreover, the 0.05Y group showed significantly higher immune-related gene (nuclear factor-kappa B, interleukin-8, and interleukin-10) mRNA expression. Altogether, our results indicate that dietary YPS supplementation enhances the antioxidant and immune capacity of M. salmoides, but with no positive effect on their growth. Full article

The presence of the white shark (Carcharodon carcharias) in the Mediterranean Sea is well documented, but mainly through historical and opportunistic records. Historically, the Adriatic Sea, particularly its eastern coastline, was considered a hotspot for white sharks, with relatively frequent reports of juvenile specimens suggesting a potential nursery area. However, since the second half of the 20th century, the abundance of white sharks in the Adriatic has experienced a dramatic decline, with the last confirmed sighting recorded in 2011. In this study, we report the recent capture of a young-of-the-year (YOY) white shark off the Croatian coast, previously misidentified as a porbeagle shark (Lamna nasus). In addition, we revisit historical records of white sharks in the Adriatic Sea to assess whether this region can be considered a nursery area. Our findings highlight significant gaps in the understanding of white shark spatial ecology and reproductive biology in the Mediterranean Sea. Furthermore, this study emphasizes the critical role citizen science and public engagement can play in documenting occurrences of these elusive and endangered predators, offering valuable insights for future conservation efforts. Full article

The coastal waters of Zhejiang feature a complex aquatic environment and abundant biological resources, creating an ideal habitat for various fish species. However, the systematic monitoring of fish larvae in these offshore waters is limited. This study collected 24,232 fish larvae using large plankton nets during April and November 2022, as well as February and July 2023, and identified 93 species, primarily warm-temperate and warm-water species, with a peak occurrence in summer. The dominant species include Larimichthys croceus, Sebastiscus marmoratus, Lateolabrax japonicus, and Odontamblyopus lacepedii, among others, and these species exhibit frequent seasonal changes. Fish larvae are typically found to be aggregated along estuaries and bays in spring, autumn, and summer, while in winter, they tend to shift towards areas near the boundaries of motor trawler fisheries areas. Our cluster analysis revealed spatial heterogeneity in the community structure, driven by an abundance of dominant and important species. Our Mantel tests and canonical correspondence analysis (CCA) identified seawater temperature and salinity as core drivers of the aggregation and distribution of fish larvae, interacting with factors such as the chlorophyll-a concentration, water turbidity, water depth, and dissolved oxygen. This research provides a scientific basis for the dynamic monitoring of spawning grounds and effective management of fishery resources in Zhejiang’s coastal waters. Full article

Monitoring stress in captive fish is crucial for their welfare, but continuous physiological measures in unrestrained animals are challenging. Rainbow trout (Oncorhynchus mykiss) exhibit divergent personalities, ranging from bold to shy, which correlate with cortisol-mediated stress responses. To determine whether personality affects the sympathetic nervous system, heart rate was measured during three potentially stressful events as a proxy for sympathetic nervous system responses. Firstly, trout were classified as bold or shy, using a novel object test. Subsequently, trout were implanted with biologgers to record heart rate in vivo at rest during and after the behavioral tests. Following recovery, the fish underwent a second novel object test, a confinement test, a pair-wise contest, and a final novel object test to explore the degree of boldness over the experimental period, which remained consistent. Heart rate was relatively higher in both bold and shy animals during the confinement test and the pair-wise contest compared with the novel object test, which indicated that heart rate monitoring was a valid gauge of the valence of the experience. Heart rate responses did not differ between bold and shy trout, indicating that behavioral phenotype did not influence the autonomic stress response. Thus, heart rate is a reliable indicator of stress without the need to account for intra-specific behavioral variations. Full article

The Australian lungfish, Neoceratodus forsteri, is one of the world’s oldest vertebrate lineages, with a slow life-history and threatened status, requiring immediate conservation efforts. The main threats to lungfish populations are degradation and availability of key macrophyte habitats, water regulation and flow modification. As this long-lived species (at least 77 years) has delayed maturity (mature at 10 years), field monitoring alone will not be enough to inform the challenge of ensuring sustainable populations. A stochastic metapopulation model was developed for the Burnett River (Southeast Queensland, Australia), an important habitat for the lungfish that is a highly regulated system with extensive water infrastructure. The model consists of three interacting populations, where the ecology and biology of the species were translated into an 80-year-class population projection matrix for each population, each with post-development streamflow, habitat and movement rules. The model highlights the longer-term interaction between dams and stream flows on habitat availability and subsequent recruitment. Through a pre-development streamflow, we quantify the impact of high regulation and development on the lungfish population in the Burnett River: a minor decline in the upstream population (e.g., 9.8% decline), a large decline in the middle population (64.2% decline), virtually no change in the downstream population (e.g., 1.2% decline) and a moderate decline in the overall metapopulation (e.g., 22.3% decline). The loss of spawning and feeding habitat remains the main reason for population decline, with implications that the loss will lead to greater pressure on remaining downstream habitat due to combined flow and dam effects and, in turn, to extended periods of recovery of spawning habitat. Our modeling approach substantially advances conservation management of this species, as it can be adapted to suit other populations in other river systems and used to test sensitivity to recovery actions. Full article

Aromatase inhibitor letrozole (LZ) and 17α-methyltestosterone (MT) are commonly used for sex control breeding to induce female-to-male sex reversal in aquaculture. However, studies on the molecular regulatory mechanisms of LZ and MT are still limited. Here, a comparative transcriptome analysis was conducted on the hypothalamus, the gonad, and the liver of golden pompano (Trachinotus ovatus) after 30 days of LZ and MT treatment, which demonstrated significant sexual size dimorphism. Following LZ treatment, the transcriptome data identified 156, 890, and 1286 different expression genes (DEGs) in the hypothalamus, the liver, and the gonad, respectively. After MT treatment, the transcriptome data identified 114, 876, and 950 DEGs in the hypothalamus, the liver, and the gonad, respectively. Functional enrichment analysis revealed that DEGs were involved in oocyte meiosis and steroid-hormone synthesis following LZ treatment. Similarly, the analysis indicated that DEGs were associated with cysteine and methionine metabolism and steroid-hormone synthesis after MT treatment. Further analysis showed that LZ treatment can promote the first meiotic division but inhibit the second meiotic division of the oocyte. MT treatment promotes polyamine synthesis to induce oocyte apoptosis, both of which affect the trajectory of ovarian differentiation in golden pompano. However, LZ and MT have converse effects in sex hormone synthesis. LZ inhibits estrogen metabolism but promotes cholesterol synthesis by regulating sqle, cyp3a40, ugt1a1, and ugt2a1, while MT promotes estrogen metabolism but inhibits the conversion of cholesterol to pregnenolone by regulating cyp19a1, cyp1a, and hsd17b7. This study reveals that both LZ and MT may inhibit the ovarian differentiation and induce masculinization through different regulatory mechanisms, which provides a fundamental insight into the sex control breeding in aquaculture. Full article

Spawning grounds may shift due to climate change and subsequent variations in the marine environment, but few studies have aimed to project shifts in the spawning grounds of chub mackerel driven by climate change. We projected the effects of climate change on the spawning grounds of chub mackerel (Scomber japonicus) by developing and applying a suitable spawning ground index based on a regional ocean circulation model for the western North Pacific. Our model indicated that the potential spawning grounds of chub mackerel extended from southern waters of the East China Sea to the Korea Strait, Yellow Sea, and Japan/East Sea. Despite some uncertainty, our model based on climate change scenarios projected that, by the 2050s, spawning grounds will shift northward due to warming of the ocean surface, resulting in a subsequent westward shift of nursery grounds from the Japan/East Sea to the Korea Strait and Yellow Sea. Our projections will contribute to clarifying the impacts of climate change on the distribution of exploitable chub mackerel, the adaptation of fisheries to climate change, and the reliability of stock assessments used for fisheries management in the region. Full article

Spotted Seatrout Cynoscion nebulosus (hereafter, trout) are one of the most heavily targeted sportfish along the Gulf coast. With recent regulation changes intended to reduce the harvest mortality of trout and promote a healthy trophy-class trout fishery in Texas, understanding differences between trophy-class (>28 in, 712 mm) and adult-class (12–28 in, 305–710) trout has become especially relevant for fisheries managers. Here, we leveraged a long-term (1983–2023) gill net dataset collected by the Texas Parks and Wildlife Department to (1) compare the distribution of size classes both spatially and temporally, (2) determine environmental drivers of the abundance of each size class, and (3) compare the species associated with each size class in the Upper Laguna Madre. Kernel density distribution estimates, hot spot analyses, and space–time pattern mining methods were used to compare the distribution of the two size classes of trout spatially and temporally. Boosted regression trees (BRTs) were used to determine the environmental drivers of abundance, and multivariate analyses were utilized to compare the species associated with each size class. Trophy-class trout exhibited a greater degree of spatial clustering than adult-class trout, with abundance peaks concentrated along specific shorelines in Baffin Bay. Significant changes in trophy-class trout distribution over time were also found, indicating that the spatial clustering of trophy-class trout has intensified over the past four decades. Salinity and bay were strong predictors for the abundance of both size classes, with peak abundances of both trophy-class and adult-class trout in Baffin Bay and its tertiary bays and at salinities of 10–30 and above 60 psu. Dissolved oxygen (DO) concentration and temperature were good predictors of the abundance of trophy-class trout, which were most abundant at temperatures of 25–30 °C and DO levels of 5–8 mg/L. Depth, turbidity, and season were good predictors of the abundance of adult-class trout, which were most abundant at increased depths (>2 m), low-to-moderate turbidity (~125 NTU), and in the spring season (April–June). Multivariate analyses revealed differences in the communities associated with trophy-class and adult-class trout occurrence, with species such as Black Drum Pogonias cromis, Striped Mullet Mugil cephalus, and Ladyfish Elops saurus more abundant in samples associated with trophy-class trout. These results indicate that trophy-class trout display unique spatial patterns and species associations and that their abundance may be driven by a distinct set of hydrological and biotic factors, which may have important implications for the management of trophy fisheries. Full article

A primary cell culture derived from the gill tissues of largemouth bass (Micropterus salmoides) was successfully established and characterized, providing a physiologically relevant model for virological research. Gill tissues were enzymatically dissociated, and their cells were cultured in M199 supplemented with 20% fetal bovine serum at 25 °C, yielding optimal growth. Viral replication within these primary cells was confirmed by transmission electron microscopy, and further qRT-PCR demonstrated the upregulation of antiviral genes (IFN1, Mx1, ISG15, and Viperin). These primary gill cells of spindle-like morphology exhibited significantly higher susceptibility to Micropterus salmoides rhabdovirus (MSRV) compared to established cell lines, as evidenced by higher viral titers, thus establishing their suitability for studying host–virus interactions. Furthermore, these cells were amenable to genetic manipulation, with the successful transfection of an mCherry reporter gene using commercially available reagents. These findings highlight the utility of the largemouth bass gill-derived primary cell culture as an alternative in vitro system for investigating MSRV pathogenesis and host immune responses, which serves as a stepping stone for improved antiviral strategies in largemouth bass aquaculture. Full article

Excess ammonia can damage the growth and development of fish. Pseudobagrus ussuriensis is a scaleless fish with important economic value that is more sensitive to ammonia stress. In this study, P. ussuriensis was explored using different ammonia concentrations [control (0 mg/L), CL; low stress (10 mg/L), T1L; and high stress (50 mg/L), T2L] for 48 h. Compared to the control group, the liver cells in the T1L group showed slight damage, while the T2L group was severely damaged, with the cells being loosely arranged, with nuclei lysis and cell vacuolization. The activities of superoxide dismutase, catalase, and glutathione in the T1L and T2L groups were significantly lower than those in the CL group (p < 0.05), and the malondialdehyde reached the maximum at 48 h. Furthermore, 9301 differentially expressed genes (DEGs) (4583 upregulated and 4718 downregulated) were detected by transcriptome sequencing. Most DEGs were highly enriched in cellular processes (GO:0009987) and cell parts (GO:0044464). Especially, the phosphatidylinositol 3-kinase/protein kinase B (PI3K-Akt) signaling pathway had the maximum quantity of DEGs in all the three groups. In-depth analysis revealed the stress caused multiple substitutions of SNP sites in pik3ca and kras, blocking the PI3K/Akt signaling pathway to prevent cancer cell proliferation and spread, accelerating the apoptosis of damaged cells. These results suggest that ammonia stress induces liver damage in P. ussuriensis, causing genetic mutations and cellular carcinogenesis, thereby accelerating cell apoptosis. Full article

In 2023, exceptionally few salmon (Salmo salar) ascended from the Baltic Sea to spawn in the Rivers Tornionjoki and Simojoki, regardless of the proper number of smolts descending to the sea in preceding years. We investigated how the numbers of age-0 and young herring (Clupea harengus) and sprat (Sprattus sprattus), which are the principal prey species of salmon in the Baltic Proper, the main feeding area of these salmon, as well as the amount of lipid obtained from them and their protein-to-lipid ratio, correlated with the number of returning salmon and the thiamine (vitamin B1) status of spawning salmon. The fewer the 0-year-old herring were and the more abundant were the youngish sprat in the Baltic Proper when the post-smolts arrived there, and the greater the lipid content and lower the protein-to-lipid ratio of the prey fish, the fewer salmon returned to the Rivers Tornionjoki and Simojoki to spawn two years later. The number of returning salmon was lowest with a high ratio of youngish sprat, 1–3 years old, regarding the River Tornionjoki and 1–2 years old regarding the River Simojoki post-smolts, to 0-year-old herring, which were of a suitable size to be the prey for the post-smolts upon their arrival in the Baltic Proper. In 2021, the ratios were lowest due to the record-low number of 0-year-old herring. The poor thiamine status of spawning salmon was also associated with the high lipid content of available prey fish and with the abundance of youngish sprat, which have twice the lipid content of age-0 herring. Our findings parallel the observations in the early 1990s when post-smolt survival declined concurrently with the outbreak of thiamine deficiency, M74. We conclude that consuming high-lipid marine fish reduces the survival of post-smolts and, thus, the number of returning salmon, in addition to causing thiamine deficiency. Full article

Vitellogenins (Vtgs) are key yolk precursor proteins in fish, serving as critical indicators of gonadal maturation in females and reliable biomarkers for detecting xeno-oestrogenic pollution, particularly through their expression in juveniles or males. The vtg gene family comprises multiple subtypes that are species-specific, necessitating precise characterisation and quantification for effective use as biomarkers in studies on estrogenic endocrine-disrupting chemicals (EEDCs). In this study, we successfully cloned and characterised the full-length cDNAs of three vtg subtypes (vtgAa, vtgAb, and vtgC) from Scatophagus argus. Differential expression analysis revealed that vtgAb exhibited the highest responsiveness to 17α-ethynylestradiol (EE2) exposure, with a 3-fold increase in vivo at 10.0 μg/g EE2 and a 30-fold increase in vitro at 10⁻⁷ mol/L EE2. The expression patterns were dose- and time-dependent, with peak expression observed 72 h post-exposure. While in vivo assays indicated moderate upregulation, in vitro experiments demonstrated significantly higher expression, attributed to direct hepatocyte interaction with EE2. These findings confirm vtgAb as the most responsive subtype to oestrogen exposure in S. argus and highlight the species’ tolerance to EE2, as compared to more sensitive species like Danio rerio. This study shows the evolutionary conservation of vtg transcripts across teleost species and reinforces the importance of subtype-specific characterisation to advance their application as biomarkers for EEDCs, with significant implications for environmental monitoring and pollution regulation. Full article

Efforts to rehabilitate habitats in trout streams are common, but the pre-and post-project monitoring of impacts has produced conflicting results. Consequently, long-term monitoring plans were established for the reaches of two streams in southeastern Minnesota, USA, that were planned for rehabilitation. Instream habitats and brown trout abundances in randomly selected sections of each rehabilitation reach were assessed for one or more years pre-project followed by multiple reoccurring surveys in the years post-rehabilitation. Significant increases in certain types of fish cover (overhanging banks, mid-channel boulders, and deep water) were observed immediately after rehabilitation in one or both streams, whereas improved channel dimensions (narrower and deeper) and hydrologic variables (higher current velocities) were less likely to be realized in the short term (1 to 4 years). Trout abundances and catch rates displayed significant year-to-year variability, but regional trout population cycles masked any true post-project increases in trout within the rehabilitated reaches. Overall, future monitoring is expected to highlight additional changes (i.e., improvements) in instream habitats as rehabilitated reaches heal and stabilize, with brown trout numbers expected to increase to higher average levels after several generations have adapted to the rehabilitated habitats. Full article

In this investigation, collagen was successfully extracted from the skin and fins of the orange-spotted grouper, Epinephelus coioides, with recovery rates of 4.45% and 23.65% (dry weight basis), respectively. UV–Vis spectrophotometric analysis demonstrated distinct absorbance peaks at 222 nm and 217 nm for collagen isolated from the skin and fins, correspondingly. Both collagen sources were confirmed to be type I, characterized by the presence of two α-chains (α1 and α2), with glycine as the predominant amino acid, an absence of tryptophan, and a notable content of proline and hydroxyproline. The enzymatic hydrolysis of fin-derived collagen using pepsin yielded low-molecular-weight peptides (PHC), which were subsequently incorporated into the diet of 1.5-year-old zebrafish, either alone or in combination with glucosamine (GC), to assess their biological effects. After eight weeks of dietary supplementation, zebrafish fed PHC or the combined PHC + GC diets exhibited a significant upregulation of sox9a (jef) expression in spinal tissues, accompanied by a marked downregulation of runx2. Although the differences in swimming performance among the groups were not statistically significant, zebrafish that received PHC or the combined supplements demonstrated enhanced endurance compared to the control group. These results suggest that collagen sourced from grouper may have advantageous effects in supporting cartilage health in aged zebrafish. Furthermore, utilizing fish by-products for collagen extraction enhances resource efficiency and aligns with circular economy principles. Full article

The purpose of this study was to investigate the physiological and biochemical changes of the hepatopancreas and intestinal microbial structure of Penaeus vannamei under various levels of carbonate alkalinity stress. After Penaeus vannamei (body length 14.24 ± 2.13 cm, body weight 26.31 ± 3.26 g) was subjected to 96 h carbonate alkalinity stress, the alkalinity stress levels were E8 (8 mmol/L), E18 (18 mmol/L) and E28 (28 mmol/L), respectively. The activity of antioxidant enzymes was determined by enzyme markers, and then the intestinal microorganisms of Penaeus vannamei were analyzed by high-throughput sequencing technology. The results showed that, under the stress of high carbonate alkalinity, the mortality rate of Penaeus vannamei was as high as 75%, and hepatopancreas cells showed obvious deformation, abnormal nuclear shapes, and serious cell vacuolation. Under high carbonate alkalinity stress, superoxide dismutase activity, catalase activity and glutathione peroxidase activity in the Penaeus vannamei hepatopancreas were significantly lower than those in control group (p < 0.05), and malondialdehyde content was significantly lower than that in the control group (p < 0.05). Alkaline phosphatase activity in the experimental group was significantly different from that in the control group (p < 0.05). Moreover, the 16SrDNA high-throughput sequencing results showed that the intestinal abundance of Proteobacteria in Penaeus vannamei was significantly decreased (p < 0.05) under high carbonate alkalinity stress, and the abundance of Bacteroides was significantly increased (p < 0.05). At the genus level, the abundance of Chrysobacteria was significantly increased (p < 0.05). The functional prediction results of COG and KEGG showed that the functional abundance of RNA polymerase sigma-70 factor is direct bacterial or plastid core RNA polymerase and is specific to promoter elements that are situated 10 and 35 base-pairs upstream of transcription-initiation points—in the high carbonate alkalinity treatment group, this was higher than that in the control group. The functional abundance of signal transduction histidine kinase was lower than that of the control group. The results of this study not only indicated that Penaeus vannamei cell structure would change and mortality would increase under high carbonate alkalinity culture environment, but they also analyzed the changes of the intestinal microbial structure under carbonate alkalinity stress. This study could provide theoretical reference for Penaeus vannamei saline–alkali land culture. Full article

This study explored the effects of replacing live fish feed with artificial compound feed on the growth performance, nutritional composition, digestive performance, and gut microbiota of Chinese giant salamander (Andrias davidianus). The experiment was divided into three groups, each with three biological replicates. The salamander juveniles were fed artificial compound feed (S), live fish (H), and frozen fish (D) for 184 days. Results showed no significant differences in growth performance among the three groups (p > 0.05). The water content in the S group was significantly higher than that in the H group (p < 0.05), and the crude fat content was slightly higher, whereas other nutritional components showed no significant differences (p > 0.05). The analysis of amino acid composition found no significant differences among the three groups of Chinese giant salamanders (p > 0.05). The analysis of fatty acid composition revealed that the feed group had significantly lower levels of polyunsaturated fatty acids compared with the other two groups (p < 0.05), and significantly higher levels of saturated fatty acids (p < 0.05). There were no significant changes in digestive enzyme activity among the three salamander groups (p > 0.05). There were also no significant differences in the remaining antioxidant indicators in the intestine and liver among the three groups of salamanders (p > 0.05). The S group had significantly higher Pielou_e and Shannon indices (p < 0.05), thereby indicating a greater diversity and evenness of the gut microbiota. In conclusion, replacing live feed with artificial compound feed does not affect the growth performance, nutritional composition, antioxidant capacity, and digestive function of Chinese giant salamander juveniles. Moreover, it enhances the diversity and richness of the gut microbiota, providing effective data to support the development of artificial feeds for giant salamanders. Full article

In order to mitigate the adverse effects of high carbohydrates on largemouth bass and to investigate the feasibility of LA as a feed additive, the present study observed the effects of added α-lipoic acid (LA) on growth performance, glucose metabolism and immunity in largemouth bass fed on high dietary carbohydrates (10% α-cassava starch inclusion). A total of 315 juvenile largemouth bass (initial body weight, 5.09 ± 0.10 g) were divided into nine tanks (800 L) (upper radius 0.65 m × lower radius 0.5 m × height 1 m), with each holding 35 fish. Three iso-nitrogenous and iso-lipidic diets supplementing with 0 g/kg, 0.5 g/kg and 1 g/kg LA (LA0, LA500, LA1000) were designed to feed juvenile largemouth bass on a satiation diet twice daily for eight weeks with each diet feeding to triplicate groups. The results indicated that the performance in growth was significantly enhanced by the addition of dietary LA (p < 0.05). Meanwhile, hepatic glycogen content was significantly reduced (p < 0.05), and the expression of genes relating to insulin pathway and glycolysis significantly increased with LA inclusion (p < 0.05). The relative expression of insulin receptor a (ira) in the LA500 group was the highest, while the relative expression of glycerol kinase (gk), phosphofructokinase liver type (pfkl) and phosphoenolpyruvate carboxykinase (pepck) was the highest in the LA1000 group (p < 0.05). In addition, LA supplementation significantly increased the activity of lysozyme, which reached its maximum value in the LA500 group (p < 0.05). LA supplementation also promoted the expression of genes relating to anti-inflammatory and inhibited the expression of pro-inflammatory related genes (p < 0.05). Above all, the dietary addition of LA could improve performance in growth, alleviated hepatic glycogen deposition, and improved the immunity function of largemouth bass fed on high dietary carbohydrates. This provides us with ideas to mitigate the adverse effects of high carbohydrates on largemouth bass in actual production and provides a basis for the application of LA in aquatic biology. Full article

To investigate the morphological traits of different sexes during the early development stage of the swimming crab Portunus trituberculatus, the genetic sex of 405 crablets from stages C I–V was determined using sex-linked molecular markers. The external appearance of each crab was observed, and the morphological traits, including carapace length (CL), full carapace width (FCW), abdomen width (AW), and abdomen length (AL), were measured to compare the differences between the sexes and to develop non-intrusive methods for sex identification. The genetic sex identification demonstrated that the female-to-male sex ratio at each stage did not deviate from 1:1. The gonopores of the females were first observed at stage C I using a scanning electron microscope; however, the shape difference in the abdominal flap between the sexes from stages C I to stage C V were not observed under a dissecting microscope. Correlation analysis showed that AW3 and AW4 were significantly correlated with sex at stage C V. Three methods were used to predict the sex of the crablets according to the morphological measurements; among them, the multinomial logistic regression (MLR) model performed better than the threshold method or the stepwise discriminant analysis, and the accuracy at stage C V increased to 90% when detailed abdominal parameters were included. These results indicate that it is feasible to predict sex during the early development stages of P. trituberculatus through morphometric and geometric parameters, which would be helpful for the creation of monosex populations of this species. Full article

This study investigated the impacts of light spectra on oxidative stress and nutrient quality of the fish Plectropomus leopardus in indoor recirculating aquaculture systems. The fish (100 g ± 0.45 g [wet weight]) were cultures in five different light spectra (full-spectrum (400–800 nm), blue (450 nm), green (530 nm), red (630 nm), and dark) for 60 days. After experimentation, blood and muscle tissue were collected and analyzed for biochemical variables and nutritional quality. We demonstrated that the total cholesterol, triglycerides activities of P. leopardus in the dark groups were substantially elevated, relative to other groups (p < 0.05). Glutathione and glutathione peroxidase activities were elevated in the green light group versus other red groups, and cortisol was drastically reduced in the red group relative to other groups (p < 0.05). The crude ash concentration in the blue and full-spectrum group was substantially more elevated than in other groups (p < 0.05). Thr, Glu, Cys, Val, Met, Ile, Leu, Phe, Lys, His, Arg were markedly higher in the blue light versus the red light group (p < 0.05). The muscle of P. leopardus was rich in lysine and its essential AA index was in the order of blue light, full-spectrum, green light, dark and red group. The content of total saturated fatty acids in the blue light group was drastically lower relative to the dark, green and red groups (p < 0.05), and the total polyunsaturated fatty acids and DHA + EPA contents in the blue light group were substantially elevated relative to the other groups (p < 0.05). These results revealed that different light environments had certain effects on blood biochemical, antioxidant capacity, nutrient composition and proportion of P. leopardus. A comprehensive evaluation found that the blue light environment had more positive effects on the physiological, biochemical and nutritional quality of P. leopardus. This result provides a theoretical reference for the lighting strategy of an indoor recirculating aquaculture system. Full article

According to European reports, the population of Anguilla anguilla has declined to unsafe biological limits in most areas and current fisheries are unsustainable. Indeed, the European eel has been listed as a critically endangered species since the 1970s and has been on the IUCN Red List of Threatened Species since 2010. Glass eel fisheries in Europe are very limited, but illegal catches and international parallel trade are major threats to eel stocks due to their high commercial value. The main hypothesis of this study is that glass eels from each estuary have unique chemical profiles according to the ecological quality of the habitat. These unique chemical fingerprints were assessed using Chemical Integrating Approaches (CIA) based on multi-element (macro, trace and ultra-trace metals), global metabolome and stable isotope analyses. Thus, CIA are intended to be an effective chemical “weapon” to (i) fingerprint wild glass eels; (ii) fingerprint captive glass eels; (iii) authenticate and trace glass eels; and (iv) combat the illegal trade in juvenile European eels. The results of this study showed that Zn and Ni can fingerprint the chemical profiles of wild and captive glass eels and their geographical origin. In the same vein, metabolomes such as Butyric acid 4-vinylphenyl ester, N-(3-carboxypropanoyl)-Met, 2-(4-Methylphenyl)acetamide, N-formyl-glutamic acid, 3-Hydroxy-2-(3-methylbutanoylamino)propanoic acid, 4-Dodecylbenzenesulfonic Acid, Arginine and Pyrazole and the stable isotope 15N show potential as a chemical tools for glass eel traceability. Full article