Fishes

17 pages, 1594 KiB

Open AccessArticle

Isolation, Identification, and Virulence Properties of Enterobacter bugandensis Pathogen from Big-Belly Seahorse Hippocampus abdominalis

by Haibin Ye, Chenhao Teng, Yueqi Yang, Yiyao Liu, Li Li, Ying Fan, Youhong Wang, Jing Diao, Lingling Yu, Chunlei Gai and Haipeng Cao

Fishes 2025, 10(8), 411; https://doi.org/10.3390/fishes10080411 - 14 Aug 2025

Abstract

Nowadays, members of the genus Enterobacter have been documented as human and aquaculture pathogens. To date, no reports have described Enterobacter bugandensis infecting Hippocampus abdominalis. In the present study, an isolate of E. bugandensis, designated H4, was identified as a causative pathogen [...] Read more.

Nowadays, members of the genus Enterobacter have been documented as human and aquaculture pathogens. To date, no reports have described Enterobacter bugandensis infecting Hippocampus abdominalis. In the present study, an isolate of E. bugandensis, designated H4, was identified as a causative pathogen in cultured H. abdominalis following Koch’s postulate, and its virulence properties were further described. The isolate’s genome consisted of a single circular chromosome and harbored several virulence and resistance genes, including, but not limited to, csgG, acrB, hcp, gndA, galF, rpoS, fur, rcsB, and phoP involved in adherence, antimicrobial activity, effector delivery systems, immune modulation, and regulation, as well as baeR, blaACT-49, ramA, hns, ftsI, acrA, gyrA, fabI, crp, oqxB, parE, gyrB, phoP, rpoB, tuf, ptsI, and fosA2 functioning against aminoglycoside, cephamycin, disinfecting agent and antiseptic, fluoroquinolone, macrolide, peptide, and other antimicrobials. Additionally, the isolate exhibited multiple resistance to cephalosporins, penicillins, and tetracyclines and demonstrated a median lethal dose (LD₅₀) of 4.47 × 10⁵ CFU/mL in H. abdominalis. To our knowledge, this is the first study to describe E. bugandensis infecting H. abdominalis. These findings highlight the zoonotic potential of E. bugandensis and underscore the need for targeted health management in seahorse farming. Full article

(This article belongs to the Special Issue Microbial Pathogens, Disease Control and Veterinary Drug Use in Aquaculture)

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21 pages, 1866 KiB

Open AccessArticle

Depletion of Albendazole and Its Metabolites and Their Impact on the Gut Microbial Community Following Multiple Oral Dosing in Yellow River Carp (Cyprinus carpio haematopterus)

by Yue Liu, Yan Dai, Yan-Ni Zhang, Wen-Rui Wang, Yu-Xin Chen, Yang-Guang Jin, Long-Ji Sun, Shi-Hao Li, Fang Yang, Xing-Ping Li and Fan Yang

Fishes 2025, 10(8), 410; https://doi.org/10.3390/fishes10080410 - 14 Aug 2025

Abstract

Healthy Yellow River carp (Cyprinus carpio haematopterus) reared at a water temperature of 23 ± 0.6 °C were orally administered albendazole (ABZ) at a dose of 12 mg/kg body weight (BW) once daily for seven consecutive days. At predetermined time points [...] Read more.

Healthy Yellow River carp (Cyprinus carpio haematopterus) reared at a water temperature of 23 ± 0.6 °C were orally administered albendazole (ABZ) at a dose of 12 mg/kg body weight (BW) once daily for seven consecutive days. At predetermined time points after the final administration, five fish were randomly selected for sampling. Plasma, skin-on-muscle, liver, and kidney tissues were collected, and the concentrations of ABZ and its three metabolites—albendazole sulfoxide (ABZSO), albendazole sulfone (ABZSO₂), and albendazole-2-aminosulfone (ABZ-2-NH₂−SO₂)—were determined using high-performance liquid chromatography (HPLC). The results indicated that ABZ and ABZSO were widely distributed across tissues, while ABZSO₂ and ABZ-2-NH₂-SO₂ were only present at trace levels. Pharmacokinetic analysis of ABZ and ABZSO in plasma and tissues was performed using noncompartmental analysis (NCA). ABZ peaked in plasma at 0.73 μg/mL at 24 h after the last administration, with an elimination half-life (t_1/2λZ) of 38.56 h. ABZSO reached a peak plasma concentration of 1.54 μg/mL at 24 h, with a t_1/2λZ of 53.73 h. According to China’s national standard, where ABZ-2-NH₂−SO₂ is the marker residue with a maximum residue limit (MRL) of 100 μg/kg in fish skin-on muscle, no withdrawal period was necessary. However, based on the European Union standard—which uses the sum of ABZ and its three metabolites as the marker residue and an MRL of 100 μg/kg in ruminants—a withdrawal period of 16 days (or 351 °C-days) was required. Additionally, the study assessed changes in the intestinal microbiota following multiple oral doses of ABZ. The results indicated that ABZ administration significantly altered microbial diversity and composition in a dose- and time-dependent manner. After drug withdrawal, the intestinal microbiota gradually returned to baseline levels, similar to the untreated control group. Full article

(This article belongs to the Special Issue Aquaculture Pharmacology)

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13 pages, 2815 KiB

Open AccessArticle

Diel Catch Variation of the Primary Fish Species Captured by Trammel Nets in a Shallow Eutrophic Lake in Jiangsu Province, China

by Jiyang Dong, Xiumiao Song, Yong Zhu, Qigen Liu and Zhongjun Hu

Fishes 2025, 10(8), 409; https://doi.org/10.3390/fishes10080409 - 14 Aug 2025

Abstract

Fish diel activity can affect the catch of fishing gear, such as gill nets, thereby influencing fishery resource assessment and management. This study investigated diel catch variations of primary fish species in Gehu Lake using monofilament trammel nets from April to November of [...] Read more.

Fish diel activity can affect the catch of fishing gear, such as gill nets, thereby influencing fishery resource assessment and management. This study investigated diel catch variations of primary fish species in Gehu Lake using monofilament trammel nets from April to November of 2016. Fish sampling occurred monthly, with nets set and fish caught at four-hour intervals in each month. The results showed that significant diel effects and diel × month interaction were found on Chinese silver carp (SC) and diel × month interaction on common carp (CC). Topmouth, humpback, and Wuchang bream (WB) displayed significantly higher catch per unit effort (CPUE) during twilight or daytime than at night, and no diel × month interactions were detected. For Chinese bighead carp (BC), Mongolian redfin (MR), Japanese grenadier anchovy (JGA), and crucian carp, no diel effect and diel × month interaction were observed. The study suggested that most activities occurring in daytime and at twilight were caused by visual orientation to prey for topmouth and humpback, and by the herbivorous feeding habitat of WB. Food competition between BC and JGA may drive a pronounced temporal partitioning of their diel activity. Overnight gillnet fishing could underestimate the population sizes of herbivores, such as WB, and visually oriented predators, for example, humpback, and might not influence the estimation for BC, JGA, and crucian carp. However, its effects on the stock estimation of SC and CC would vary with months. Notably, future winter investigations into diel catch in this lake could potentially augment the conclusions of the present study. Full article

(This article belongs to the Special Issue Biodiversity and Spatial Distribution of Fishes, Second Edition)

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15 pages, 2124 KiB

Open AccessArticle

Rutin Inhibits Histamine-Induced Cytotoxicity of Zebrafish Liver Cells via Enhancing Antioxidant and Anti-Inflammatory Properties

by Ke Cheng, Apeng Liu, Di Peng, Lixue Dong, Yangyang Liu, Juan Tian, Hua Wen, Yongju Luo, Zhongbao Guo and Ming Jiang

Fishes 2025, 10(8), 408; https://doi.org/10.3390/fishes10080408 - 14 Aug 2025

Abstract

Histamine can damage the antioxidant and immune systems in fish and crustaceans. Rutin, a natural substance with a diverse phenolic structure, has demonstrated antioxidant and anti-inflammatory properties. However, whether rutin can mitigate histamine-induced negative effects remains uninvestigated in fish models. This study investigated [...] Read more.

Histamine can damage the antioxidant and immune systems in fish and crustaceans. Rutin, a natural substance with a diverse phenolic structure, has demonstrated antioxidant and anti-inflammatory properties. However, whether rutin can mitigate histamine-induced negative effects remains uninvestigated in fish models. This study investigated the effect of 0.1–100 μM rutin preincubation on histamine (29.5 mM)-induced cytotoxicity in zebrafish liver cells (ZFL) and its potential mechanisms. Results showed that 0.1–100 μM rutin significantly improved ZFL cell survival following histamine stimulation and protected cellular morphology. Rutin inhibited the adverse effects of histamine on ZFL by scavenging or suppressing the accumulation of reactive oxygen species (ROS), H₂O₂, and malondialdehyde (MDA), while increasing the activities of superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity (T-AOC). At the protein level, 10 μM rutin significantly promoted Nrf2 protein expression. HO-1 protein was significantly up-regulated after preincubation with 0.1–10 μM rutin, whereas IL-1β protein levels were significantly down-regulated. The mechanism may involve activation of the Nrf2 antioxidant signaling pathway and inhibition of the NF-κB inflammatory signaling pathway. In summary, within the experimental concentration range, 10 μM rutin showed the strongest inhibitory effects on histamine-induced ZFL cell death and oxidative stress. This study provides a theoretical basis and data support for evaluating rutin’s feasibility as a green aquatic feed additive. Full article

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16 pages, 4236 KiB

Open AccessArticle

Toxic Effects of Tetramethyl Bisphenol A on Embryonic–Larval Development of Zebrafish (Danio rerio)

by Ermei Yin, Manwen Zeng, Haipeng Yan, Jiahao Gao, Zuchun Chen, Ning Zhang, Yusong Guo, Zhongduo Wang and Zhongdian Dong

Fishes 2025, 10(8), 407; https://doi.org/10.3390/fishes10080407 - 14 Aug 2025

Abstract

Tetramethyl bisphenol A (TMBPA), a novel alternative to Bisphenol A, is widely used as an industrial flame retardant and a raw material for tetramethyl polycarbonate plastics. With the increasing use of TMBPA, its aquatic ecological risks remain unclear. Therefore, this study investigated the [...] Read more.

Tetramethyl bisphenol A (TMBPA), a novel alternative to Bisphenol A, is widely used as an industrial flame retardant and a raw material for tetramethyl polycarbonate plastics. With the increasing use of TMBPA, its aquatic ecological risks remain unclear. Therefore, this study investigated the developmental toxicity of TMBPA using zebrafish (Danio rerio) as a model, exposing embryos to 0.5, 5, 50, and 200 μg/L TMBPA for 120 h. The results showed that treatment with 5, 50, and 200 μg/L TMBPA decreased the hatching rate of zebrafish embryos at 48 h post-fertilization (hpf), while no significant difference was observed at 72 hpf. Meanwhile, TMBPA exposure at all concentrations showed no significant effect on the survival rate. Furthermore, a high concentration of TMBPA (200 μg/L) significantly reduced the total length and suppressed swimming ability in zebrafish larvae. In addition, gene expression analysis revealed impacts on antioxidant system (cat, gpx, mn-sod, keap1, ucp2, nrf2), hypothalamic–pituitary–thyroid (HPT) axis (ttr, ugt1ab, trβ), cardiac developmental (tbx2b, myl7, bmp4, notch1b, amhc), and the hypothalamic–pituitary–adrenal (HPA) axis (pomca and nr3c1). The results indicated that TMBPA exposure adversely disrupted embryo hatching and larval development of zebrafish, accompanied by altering the expression of functional genes in larvae. These results provide further evidence for the potential environmental hazard posed by TMBPA. Full article

(This article belongs to the Section Environment and Climate Change)

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19 pages, 1619 KiB

Open AccessArticle

Impact of Water Velocity on Litopenaeus vannamei Behavior Using ByteTrack-Based Multi-Object Tracking

by Jiahao Zhang, Lei Wang, Zhengguo Cui, Hao Li, Jianlei Chen, Yong Xu, Haixiang Zhao, Zhenming Huang, Keming Qu and Hongwu Cui

Fishes 2025, 10(8), 406; https://doi.org/10.3390/fishes10080406 - 14 Aug 2025

Abstract

In factory-controlled recirculating aquaculture systems, precise regulation of water velocity is crucial for optimizing shrimp feeding behavior and improving aquaculture efficiency. However, quantitative analysis of the impact of water velocity on shrimp behavior remains challenging. This study developed an innovative multi-objective behavioral analysis [...] Read more.

In factory-controlled recirculating aquaculture systems, precise regulation of water velocity is crucial for optimizing shrimp feeding behavior and improving aquaculture efficiency. However, quantitative analysis of the impact of water velocity on shrimp behavior remains challenging. This study developed an innovative multi-objective behavioral analysis framework integrating detection, tracking, and behavioral interpretation. Specifically, the YOLOv8 model was employed for precise shrimp detection, ByteTrack with a dual-threshold matching strategy ensured continuous individual trajectory tracking in complex water environments, and Kalman filtering corrected coordinate offsets caused by water refraction. Under typical recirculating aquaculture system conditions, three water circulation rates (2.0, 5.0, and 10.0 cycles/day) were established to simulate varying flow velocities. High-frequency imaging (30 fps) was used to simultaneously record and analyze the movement trajectories of Litopenaeus vannamei during feeding and non-feeding periods, from which two-dimensional behavioral parameters—velocity and turning angle—were extracted. Key experimental results indicated that water circulation rates significantly affected shrimp movement velocity but had no significant effect on turning angle. Importantly, under only the moderate circulation rate (5.0 cycles/day), the average movement velocity during feeding was significantly lower than during non-feeding periods (p < 0.05). This finding reveals that moderate water velocity constitutes a critical hydrodynamic window for eliciting specific feeding behavior in shrimp. These results provide core parameters for an intelligent Litopenaeus vannamei feeding intensity assessment model based on spatiotemporal graph convolutional networks and offer theoretically valuable and practically applicable guidance for optimizing hydrodynamics and formulating precision feeding strategies in recirculating aquaculture systems. Full article

(This article belongs to the Special Issue Application of Artificial Intelligence in Aquaculture)

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19 pages, 3707 KiB

Open AccessArticle

The Effect of a Polypeptide Based Vaccine on Fish Welfare and Infestation of Salmon Lice, Lepeophtheirus salmonis, in Sea Cages with Atlantic Salmon (Salmo salar L.)

by Ragnar Nortvedt, Erik Dahl-Paulsen, Laura Patricia Apablaza Bizama, Amritha Johny and Erik Slinde

Fishes 2025, 10(8), 405; https://doi.org/10.3390/fishes10080405 - 13 Aug 2025

Abstract

A new polypeptide vaccine towards salmon lice (Lepeophtheirus salmonis) was given to experimental groups of 2 × 8000 Atlantic salmon parr (Salmo salar L.), following the vaccination of a total of 4 × 8000 parr with a common set of [...] Read more.

A new polypeptide vaccine towards salmon lice (Lepeophtheirus salmonis) was given to experimental groups of 2 × 8000 Atlantic salmon parr (Salmo salar L.), following the vaccination of a total of 4 × 8000 parr with a common set of vaccines used in Norwegian aquaculture to prevent infestation in salmon growing at sea. The remaining 2 × 8000 salmon served as control. The trial was conducted at a sea farm research facility at Knappen-Solheim in Masfjorden, Norway. Natural infestation with sea lice were staged and counted once a week from January–December 2023. The infestation was never above two mature female lice per salmon, the maximum limit set specifically for the present trial by the Norwegian Food Safety Authorities, thus delousing with chemicals or other methods was avoided. Mortality, growth, feed consumption, sexual maturation, slaughter quality, and welfare quality parameters were not significantly different between vaccinated and control salmon. The effect size showed a moderate positive difference of 0.07 mature female salmon lice per salmon in favor of the vaccinated groups from a fish size above 600 g in May until November. All fish were slaughtered and marketed at a size of 5.8 kg (>83% superior quality). Full article

(This article belongs to the Special Issue Healthy Aquaculture and Disease Control)

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17 pages, 2243 KiB

Open AccessArticle

Long-Term Changes in Fish Landings and Fish Community Structure in Nile Delta Lakes: Implications for Fisheries Sustainability

by Mohamed Samy-Kamal and Ahmed A. Abdelhady

Fishes 2025, 10(8), 404; https://doi.org/10.3390/fishes10080404 - 13 Aug 2025

Abstract

This study examined long-term trends (1991–2019) in landings and fish community structure in the four Egyptian Nile Delta lakes. Using fisheries data, we explored trends in the catch per unit effort (CPUE) and temporal dynamics of landings and fishing effort. Non-metric Multidimensional Scaling [...] Read more.

This study examined long-term trends (1991–2019) in landings and fish community structure in the four Egyptian Nile Delta lakes. Using fisheries data, we explored trends in the catch per unit effort (CPUE) and temporal dynamics of landings and fishing effort. Non-metric Multidimensional Scaling (nMDS) and Similarity Percentage Analysis (SIMPER) were employed to assess long-term changes in fish community structure. The results revealed variable productivity across the lakes. Lake Manzala often exhibited higher yields between 1991 and 2004, and notably in 2013 (e.g., 62,372 tons), while Lake Burullus peaked at 81,399 tons in 2019. A reciprocal trend was often observed in their total yields. Lake Burullus catches were dominated by Tilapia and Mullets, while Edku and Mariout showed lower productivity. CPUE patterns varied, with Lake Manzala showing a notable increase, peaking at approximately 52 tons per boat per year in 2013, and Lake Burullus experienced a sharp increase to about 29 tons per boat per year in 2019. A shift towards amateur fishing was observed predominantly in Lake Manzala, alongside a decline in traditional licensing. An increase in fishers operating without boats was also noted across all the Northern Lakes, with contributions from Lake Edko and Lake Manzala. nMDS and SIMPER analyses revealed distinct temporal groupings of years within each lake, indicating significant shifts in fish community structure, likely in response to invasive species, pollution, and habitat degradation. These findings underscore the need for lake-specific management and long-term monitoring to address unsustainable fishing and ecological changes, ensuring biodiversity conservation and fisheries sustainability in the region. Full article

(This article belongs to the Special Issue Sustainable Management of Small-Scale and Data-Limited Fisheries: Diagnosis and Strategies)

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12 pages, 498 KiB

Open AccessArticle

A Kinetic Study on the Accumulation of No.0 Fuel Oil and Pinghu Crude Oil Water-Accommodated Fraction in Exopalaemon carinicauda

by Lei Li, Yiyun Zhang, Li Wei, Aijia Lin, Jiaying Cai, Zengqiao Wei, Qingyuan Wu, Junxiang Niu, Yanming Sui and Mei Jiang

Fishes 2025, 10(8), 403; https://doi.org/10.3390/fishes10080403 - 13 Aug 2025

Abstract

The kinetic parameters of No.0 fuel oil and Pinghu crude oil water-accommodated fractions (WAFs) during accumulation and elimination in Exopalaemon carinicauda were quantified using a semi-static two-compartment kinetic model. The accumulation phase data were analyzed via nonlinear regression to obtain kinetic parameters, yielding [...] Read more.

The kinetic parameters of No.0 fuel oil and Pinghu crude oil water-accommodated fractions (WAFs) during accumulation and elimination in Exopalaemon carinicauda were quantified using a semi-static two-compartment kinetic model. The accumulation phase data were analyzed via nonlinear regression to obtain kinetic parameters, yielding critical values including the uptake rate constant (k₁), elimination rate constant (k₂), bioconcentration factor (BCF), equilibrium body burden (C_A_max), and biological half-life (B_1/2). Modeling results demonstrated distinct kinetic parameters for the two oils. For No.0 fuel oil, the average values were k₁ = 5.21; k₂ = 0.1105; BCF = 48.98; C_A_max = 2.95 mg/kg; and B_1/2 = 6.40 days. For Pinghu crude oil, the averages were k₁ = 10.25; k₂ = 0.1044; BCF = 98.15; C_A_max = 8.48 mg/kg; and B_1/2 = 6.64 days. The uptake rate constant (k₁) and BCF generally decreased with increasing petroleum hydrocarbon exposure concentrations in ambient seawater, while the elimination rate constant (k₂) remained relatively constant across different concentrations. C_A_max increased proportionally with the petroleum hydrocarbon exposure concentration. Goodness-of-fit tests confirmed that the petroleum hydrocarbon concentrations in the experimental data were well described by the semi-static two-compartment model. Throughout the testing period, the concentration of No.0 fuel oil in Exopalaemon carinicauda remained lower than that of Pinghu crude oil. Full article

(This article belongs to the Section Environment and Climate Change)

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16 pages, 1640 KiB

Open AccessArticle

Ontogenetic and Sex-Specific Isotopic Niches of Blue Sharks (Prionace glauca) in the Northwestern Pacific

by Pengpeng Ding, Satoshi Katayama, Hiroaki Murakami and Tah Andrew Ryan

Fishes 2025, 10(8), 402; https://doi.org/10.3390/fishes10080402 - 12 Aug 2025

Abstract

The blue shark (Prionace glauca) is a pelagic species widely distributed in the northwestern Pacific Ocean. The trophic roles of blue sharks across different developmental stages and between sexes remain poorly understood. Fifty-four sharks were sampled (October 2022–March 2024) for precaudal [...] Read more.

The blue shark (Prionace glauca) is a pelagic species widely distributed in the northwestern Pacific Ocean. The trophic roles of blue sharks across different developmental stages and between sexes remain poorly understood. Fifty-four sharks were sampled (October 2022–March 2024) for precaudal length (PCL) and stable isotope levels (δ¹³C, δ¹⁵N) in the muscle tissue (n = 52). Mean PCL varied based on the month of sampling (p = 0.034), with the smallest individuals occurring in July (143.0 ± 4.3 cm) and the largest in October (178.0 ± 2.6 cm). Stable isotope analysis (δ¹³C and δ¹⁵N) indicated consistent offshore habitat use (δ¹³C: from −20.70 to −18.82‰) and significant nitrogen isotopic differences among life history (δ¹⁵N: from 10.23 to 15.72‰; Kruskal–Wallis test, p = 0.037). The elevated δ¹⁵N values observed in the subadult group (relative to juvenile individuals) are likely due to trophic enrichment associated with morphological development. Females exhibited markedly larger isotopic niches (SEAc = 2.42‰²) than did males (0.57‰²), and niche overlap was greater within each sex (40–52%) than between sexes (<21%). These results revealed sex-specific ecological roles and trophic strategies throughout the life history of P. glauca. Understanding these foraging differences can help with catch reduction and habitat-protection measures in the transboundary pelagic fisheries of the northwestern Pacific. Full article

(This article belongs to the Section Biology and Ecology)

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12 pages, 1701 KiB

Open AccessArticle

Smaller Body Size and Warmer Water Improve Two Temperate Fishes’ Upstream Passage over Wetted Ramps

by Uli Reinhardt and Grace Scott Halcrow

Fishes 2025, 10(8), 401; https://doi.org/10.3390/fishes10080401 - 11 Aug 2025

Abstract

Most artificial fishways allow upstream passage of large-bodied, strong-swimming fish species. Wetted ramps, which are moderate in inclination and have little water flow, could allow passage of smaller-bodied fishes over low-head dams and culverts. We observed creek chubs (Semotilus atromculatus) and [...] Read more.

Most artificial fishways allow upstream passage of large-bodied, strong-swimming fish species. Wetted ramps, which are moderate in inclination and have little water flow, could allow passage of smaller-bodied fishes over low-head dams and culverts. We observed creek chubs (Semotilus atromculatus) and white suckers (Catostomus commersonii) on wetted ramps in a laboratory setting. Smaller individuals entered the ramps at lower absolute swim velocities but exhibited superior upstream passage due to positive acceleration in the thin (<1 cm) water layer on the ramps. Larger fish displayed more pronounced, probably less efficient, head and tail amplitudes during passage. We argue that the relatively smaller depth of immersion in water was responsible for hampering the larger-bodied individuals on the ramps. Warmer water temperatures (15 °C vs. 10 °C) roughly doubled the mean distance fish traveled up the ramps. Our findings can inform fishway design for small-bodied fishes. In regions with low-head barriers against invasive sea lamprey (Petromyzon marinus), wetted ramps may help connect habitats for native fish species. Full article

(This article belongs to the Special Issue New Conservation Strategies for Freshwater and Marine Fishes: Habitat Is the Key)

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16 pages, 3173 KiB

Open AccessArticle

A Quantitative Approach to Prior Setting for Relative Biomass (B/k) in CMSY++: Application to Snow Crabs (Chionoecetes opilio) in Korean Waters

by Ji-Hyun Eom, Sung-Il Lee and Sang-Chul Yoon

Fishes 2025, 10(8), 400; https://doi.org/10.3390/fishes10080400 - 11 Aug 2025

Abstract

Snow crabs (Chionoecetes opilio), a commercially valuable species in Korean waters, have been managed under the Total Allowable Catch (TAC) system since 2002. However, stock assessment has been limited due to difficulties in estimating key ecological traits such as growth, maturity, [...] Read more.

Snow crabs (Chionoecetes opilio), a commercially valuable species in Korean waters, have been managed under the Total Allowable Catch (TAC) system since 2002. However, stock assessment has been limited due to difficulties in estimating key ecological traits such as growth, maturity, and mortality. In this study, the Bayesian Schaefer Model (BSM), implemented within CMSY++ framework, was applied to assess the stock status of snow crabs in Korean waters. BSM requires catch and abundance index data, such as catch per unit effort (CPUE) or biomass, as well as prior information on species resilience and relative biomass (B/k). To improve the reliability of B/k priors, we developed a method to calculate them quantitatively using fishery data, sales amounts, and biological information, unlike the qualitative assumptions on stock and fishing conditions proposed in previous research. Two standardized CPUE indices with differing temporal trends in recent years were used as abundance indices. To address the structural uncertainty associated with these divergent trends, we applied a grid-based approach by treating each CPUE index as an independent model scenario and integrating the posterior distributions. A total of 12,000 posterior estimates (6000 per index) were generated through the BSM and used to construct a Kobe plot. Results indicate that the current biomass is slightly above the level supporting maximum sustainable yield, and fishing mortality slightly below the optimal level, suggesting that the stock is healthy and sustainably exploited. Future research should aim to establish a systematic framework for developing quantitative B/k priors to enhance stock assessment accuracy. Full article

(This article belongs to the Special Issue Modeling Approach for Fish Stock Assessment)

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15 pages, 1768 KiB

Open AccessArticle

Analysis of Morphological Characteristics of Male and Female Gymnocypris eckloni Herzenstein

by Qiming Wang, Suxing Fu, Xiaoyi Chen, Yuting Duan, Luo Lei, Yawen Fan and Chaowei Zhou

Fishes 2025, 10(8), 399; https://doi.org/10.3390/fishes10080399 - 8 Aug 2025

Abstract

Accurate sex identification is crucial for the artificial breeding of fish species, and identification based on phenotypic traits is the preferred method owing to its low cost and rapidity. This study aimed to investigate morphological differences between male and female Gymnocypris eckloni Herzenstein. [...] Read more.

Accurate sex identification is crucial for the artificial breeding of fish species, and identification based on phenotypic traits is the preferred method owing to its low cost and rapidity. This study aimed to investigate morphological differences between male and female Gymnocypris eckloni Herzenstein. A total of 166 G. eckloni individuals (83 males and 83 females) were included, and 20 morphological indicators, including head length, snout length, and body weight, were measured. Various analytical methods, such as correlation analysis, principal component analysis, discriminant analysis, and systematic cluster analysis, were used to compare the morphological characteristics of male and female G. eckloni. The result showed significant differences in morphological characteristics between male and female individuals (p ≤ 0.05). Principal component analysis revealed five main components that collectively contributed to 83.64% of the variance, primarily including body length, fork length, total length, and body weight, highlighting the significance of these components in sex differentiation. Subsequently, a mathematical model was constructed via discriminant analysis. This model demonstrated an accuracy of 79.5% and 73.5% in identifying male and female G. eckloni, respectively, with an overall accuracy of 76.50%. Furthermore, on analyzing the relationship between body length and body weight in G. eckloni, we found differences in growth patterns between sexes. In particular, female fish usually weighed more than male fish, which was consistent with the biological characteristics and energy distribution patterns of G. eckloni. These results suggest that sexual dimorphism in G. eckloni is primarily concentrated in body shape and head morphology, which provides a reliable basis for sex identification based on morphological differences. Full article

(This article belongs to the Section Sustainable Aquaculture)

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17 pages, 1795 KiB

Open AccessArticle

Facilitation and Interference Between Native Fishes Influence Invasion Resistance

by Jeffrey E. Hill and Theresa P. Floyd

Fishes 2025, 10(8), 398; https://doi.org/10.3390/fishes10080398 - 8 Aug 2025

Abstract

Understanding the dynamics of species invasions in aquatic ecosystems is crucial for conservation and management efforts. We investigated the influence of species interactions and habitat complexity on biotic resistance to invasion by small-bodied freshwater fishes in peninsular Florida. Specifically, we focused on the [...] Read more.

Understanding the dynamics of species invasions in aquatic ecosystems is crucial for conservation and management efforts. We investigated the influence of species interactions and habitat complexity on biotic resistance to invasion by small-bodied freshwater fishes in peninsular Florida. Specifically, we focused on the interactions between two native species, Florida bass (Micropterus salmoides) and eastern mosquitofish (Gambusia holbrooki), and a common invader, the green swordtail (Xiphophorus hellerii). Our experiments included tanks with varying levels of structural complexity to mimic different habitat types. The presence of both native species significantly reduced swordtail survival, but the effect varied depending on habitat complexity. In habitats with strong predation refuge, mosquitofish facilitated bass predation on swordtails, whereas in habitats with weak predation refuge, bass suppressed mosquitofish aggression, leading to interference. Mosquitofish predominantly occupied vegetated areas and aggressively interacted with swordtails, significantly reducing invader survival. Our findings highlight the importance of considering species interactions and habitat complexity in predicting biotic resistance to invasions. We conclude that diverse interactions among native species can either enhance or impede invasion resistance, with implications for conservation and management strategies. Further research is needed to understand the broader impacts of multiple predators and competitors on invader dynamics in aquatic ecosystems. Full article

(This article belongs to the Section Biology and Ecology)

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16 pages, 6802 KiB

Open AccessArticle

Morphomolecular Characterization of Rhadinorhynchus niloticus (Acanthocephala: Rhadinorhynchidae) from Nile Perch (Lates niloticus, Perciformes: Latidae)

by Ebtsam Sayed Hassan Abdallah, Marco Albano and Hasnaa Thabit

Fishes 2025, 10(8), 397; https://doi.org/10.3390/fishes10080397 - 8 Aug 2025

Abstract

Adults of Rhadinorhynchus niloticus, a member of the Rhadinorhynchidae family, were isolated from the intestines of wild Nile perch (Lates niloticus (Linnaeus, 1758); Perciformes: Latidae) caught from the River Nile and its tributaries in Assiut City, Egypt. The parasite was found [...] Read more.

Adults of Rhadinorhynchus niloticus, a member of the Rhadinorhynchidae family, were isolated from the intestines of wild Nile perch (Lates niloticus (Linnaeus, 1758); Perciformes: Latidae) caught from the River Nile and its tributaries in Assiut City, Egypt. The parasite was found freely in the intestinal lumen with a prevalence of 10.71%, and the burden varied from one to five parasites per fish. The mean intensity and abundance were 2.16 ± 0.47 (95% CI: 1.33 to 3.17) and 0.23 ± 0.08 (95% CI: 0.11 to 0.43), respectively. The parasite was described using light and scanning electron microscopy. Molecular species identification as well as phylogenetic relationship analysis of the isolated parasite were achieved by sequencing and comparisons of the mitochondrial cytochrome oxidase C subunit I (COI) and nuclear 18S rRNA genes. The sequences were deposited in GenBank under the accession numbers PP859185 and MZ727194. Furthermore, phylogenetic analysis demonstrated that the parasites emerged from a separate branch belonging to the Rhadinorhynchidae family, which was clearly distinguished from other genospecies. Full article

(This article belongs to the Special Issue Advances in Fish Pathology and Parasitology)

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19 pages, 30477 KiB

Open AccessArticle

Impact of Novel Diets on the Distribution of Mucosal Immune Cells in the Digestive System of High-Growth Genetically Selected Gilthead Seabream (Sparus aurata) in a Long-Term Feeding Trial

by Sirine Abdeljaouad, Paula Sarmiento, Rafael Ginés, Gabriela Duque and Pedro L. Castro

Fishes 2025, 10(8), 396; https://doi.org/10.3390/fishes10080396 - 8 Aug 2025

Abstract

An alternative fish feed (ALT) replacing 50% of the fishmeal with poultry byproduct meal and insect meal and total fish oil with microalgae, poultry, and salmon byproducts oils was tested for 300 days on 900 gilthead seabream (Sparus aurata) with an [...] Read more.

An alternative fish feed (ALT) replacing 50% of the fishmeal with poultry byproduct meal and insect meal and total fish oil with microalgae, poultry, and salmon byproducts oils was tested for 300 days on 900 gilthead seabream (Sparus aurata) with an initial body weight of 17.1 ± 1.8 g (mean ± SD) of unselected (REF) and selected (HG) genotypes. Using in situ, histochemistry, and immunohistochemistry techniques, we assessed the immune response by characterizing IgT and IgM immunoglobulins, CD3ε⁺ T lymphocytes, and eosinophilic granular cells (EGCs) along the digestive system. IgT mRNA⁺ cells were concentrated in the second part of the digestive tract, while IgM⁺ predominated in the first and occasionally showed intraepithelial localization. CD3ε⁺ and EGCs were most prominent in the midgut. The diet affected IgT and IgM mRNA⁺ cells mainly in the initial part of the digestive tract. For CD3ε⁺, the diet only affected the initial and final parts, while the ALT diet increased EGC abundance across the middle compartments. Genetic selection had minimal effect on IgT⁺ and CD3ε⁺ cells, affecting only the first compartments. The REF group showed higher IgM⁺ cell abundance in specific regions, while EGCs differed between genotypes, favoring anterior accumulation in HG and ileocecal abundance in the REF group. Full article

(This article belongs to the Section Nutrition and Feeding)

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12 pages, 1451 KiB

Open AccessArticle

First Morphological and Molecular Identification of Intestinal Helminths in Wild Turbot Scophthalmus maximus (Linnaeus, 1758) Along the Bulgarian Black Sea Coast

by Alexander Atanasoff, Cigdem Urku, Elitsa Petrova-Pavlova and Feriha Tserkova

Fishes 2025, 10(8), 395; https://doi.org/10.3390/fishes10080395 - 7 Aug 2025

Abstract

Turbot Scophthalmus maximus (Linnaeus, 1758) is one of the most valuable and economically important species for the Black Sea countries. In Bulgaria, their numbers are limited and stocks are depleted; therefore, monitoring development and health status is extremely important. Internal helminths are widespread [...] Read more.

Turbot Scophthalmus maximus (Linnaeus, 1758) is one of the most valuable and economically important species for the Black Sea countries. In Bulgaria, their numbers are limited and stocks are depleted; therefore, monitoring development and health status is extremely important. Internal helminths are widespread among turbots on the Bulgarian Black Sea coast. However, description of this infection is relatively limited, and they have not been reported in scientific papers. For this purpose, a total of 36 hauls were made at depths from 15 to 90 m, and 65 turbots were examined for intestinal parasites. The present study represents the first report of internal helminths in turbot from Bulgarian marine waters through the spawning season, characterized morphologically based on a microscope observation and molecular identification. Evaluation of laboratory analyses revealed that two different parasites were determined: Bothriocephalus sp. (Müller, 1776) and Hysterothylacium aduncum (Rudolphi, 1802) and that 73.85% of the turbot were infected with one or more parasites. Based on the results, control measures and treatment for the wild population are unrealistic but should be considered for the containment and spread of diseases in aquaculture facilities. Full article

(This article belongs to the Special Issue Advances in Fish Pathology and Parasitology)

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15 pages, 662 KiB

Open AccessArticle

Genetic Structuring and Connectivity of European Squid Populations in the Mediterranean Sea Based on Mitochondrial COI Data

by Vasiliki Pertesi, Joanne Sarantopoulou, Athanasios Exadactylos, Dimitrios Vafidis and Georgios A. Gkafas

Fishes 2025, 10(8), 394; https://doi.org/10.3390/fishes10080394 - 7 Aug 2025

Abstract

Understanding population connectivity and genetic structure is crucial for the effective management of exploited marine species. This study investigates the population genetics of the common European squid (Loligo vulgaris) across the Mediterranean Sea, focusing on samples from the Aegean Sea and [...] Read more.

Understanding population connectivity and genetic structure is crucial for the effective management of exploited marine species. This study investigates the population genetics of the common European squid (Loligo vulgaris) across the Mediterranean Sea, focusing on samples from the Aegean Sea and comparative sequences from Western Mediterranean, Eastern Mediterranean, and Atlantic coasts. A total of 67 COI mitochondrial sequences were analyzed, identifying 12 haplotypes and 27 polymorphic sites. Population-level genetic diversity, pairwise F_ST values, and haplotype network analyses revealed pronounced genetic differentiation in the eastern Mediterranean contrasting with the genetic homogeneity observed among Western populations. The low haplotype diversity observed in the Greek populations of L. vulgaris may be influenced by a combination of ecological and historical factors, as the Aegean region is recognized as a hotspot of endemism and historical population fragmentation. The results indicate the existence of at least two genetically differentiated clusters within the Mediterranean basin. This study advances current knowledge of the genetic structure of Loligo vulgaris by providing novel genetic data on populations from the eastern Mediterranean, offering valuable insights for future conservation and management strategies for the species. Full article

(This article belongs to the Section Genetics and Biotechnology)

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20 pages, 3615 KiB

Open AccessArticle

Identification of Suitable Habitats for Threatened Elasmobranch Species in the OSPAR Maritime Area

by Moritz Mercker, Miriam Müller, Thorsten Werner and Janos Hennicke

Fishes 2025, 10(8), 393; https://doi.org/10.3390/fishes10080393 - 7 Aug 2025

Abstract

Protecting threatened elasmobranch species despite limited data on their distribution and abundance is a critical challenge, particularly in the context of increasing human impacts on marine ecosystems. In the northeastern Atlantic, species such as the leafscale gulper shark, Portuguese dogfish, spurdog, and spotted [...] Read more.

Protecting threatened elasmobranch species despite limited data on their distribution and abundance is a critical challenge, particularly in the context of increasing human impacts on marine ecosystems. In the northeastern Atlantic, species such as the leafscale gulper shark, Portuguese dogfish, spurdog, and spotted ray are facing pressures from overfishing, bycatch, habitat degradation, and climate change. The OSPAR Commission has listed these species as threatened and/or declining and aims to protect them by reliably identifying suitable habitats and integrating these areas into Marine Protected Areas (MPAs). In this study, we present a spatial modelling framework using regression-based approaches to identify suitable habitats for these four species. Results show that suitable habitats of the spotted ray (25.8%) and spurdog (18.8%) are relatively well represented within existing MPAs, while those of the deep-water sharks are underrepresented (6.0% for leafscale gulper shark, and 6.8% for Portuguese dogfish). Our findings highlight the need for additional MPAs in deep-sea continental slope areas, particularly west and northwest of Scotland and Ireland. Such expansions would support OSPAR’s goal to protect 30% of its maritime area by 2030 and could benefit broader deep-sea biodiversity, including other vulnerable demersal species and benthic communities. Full article

(This article belongs to the Special Issue Habitat Assessment and Conservation of Fishes)

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