Fishes

Freshwater ecosystems are increasingly stressed by drought and anthropogenic inputs that can increase specific conductivity (SPC) and pH; however, little is known about how harsher conditions affect fish. We evaluated how fish growth and diet composition changed along a natural gradient in SPC and pH in Wyoming, USA using Northern plains killifish (Fundulus kansae) and Fathead minnows (Pimephales promelas). We surveyed 201 sites where we measured water chemistry, sampled fish, and assessed invertebrate prey availability from May to September 2024. Northern plains killifish and/or Fathead minnows inhabited 12 sites, which were the focus of our study. We measured otoliths to assess growth and stomach contents to estimate dietary selectivity. Growth decreased at higher SPC (486–23,500 µS/cm) for Fathead minnows and pH (7.2–9.0) for both species, suggesting an energy trade-off with osmoregulation. Dietary analyses revealed variable selection for Chironomidae larvae, while other taxa such as Gammaridae and Coleoptera were avoided at higher SPC and pH. Despite the extreme conditions, these fish maintained some dietary preference, highlighting behavioral plasticity. Our findings suggest that while these species can tolerate harsh environments, sublethal effects on growth and diet may limit long-term fitness. This research offers a framework for assessing the viability of fish populations inhabiting ecosystems with increasing salinity and pH that can inform conservation and management strategies under future environmental change. Full article

Nuclear factors of activated T cells (NFATs) are pivotal regulatory factors of immune responses, primarily by modulating T cell activity and regulating inflammatory cytokine gene transcription. The grass carp reovirus (GCRV) triggers a serious hemorrhagic condition, posing a significant threat to sustainable grass carp (Ctenopharyngodon idella) aquaculture. However, the precise function of NFAT in the host’s defense against GCRV infection is mostly undefined. This study comprehensively identified and characterized the NFAT genetic family in grass carp, cloned grass carp NFAT1 (CiNFAT1), and investigated its expression and function during GCRV infection. Eight NFAT genes encoding seventeen isoforms have been detected within the grass carp’s genomic sequence, distributed across six different chromosomes. Comparative analysis revealed homology with zebrafish NFATs. CiNFAT1 possesses a 2697 bp open reading frame, encoding 898 amino acids, and contains conserved Rel homology domain (RHD) and NFAT-homology (IPT) domains. Quantitative PCR (qPCR) revealed ubiquitous CiNFAT1 expression in healthy grass carp tissues, with the highest expression in gills and skin and the lowest in liver. Following GCRV challenge in vivo, CiNFAT1 expression in immune tissues (liver, spleen, kidney, gill, intestine) showed dynamic changes over time. In vitro experiments in CIK cells demonstrated that CiNFAT1 expression peaked at 12 h post-GCRV infection. Further functional studies revealed that overexpression of CiNFAT1 significantly reduced GCRV replication at 36 h post-infection. This reduction was accompanied by elevated expression of type I interferon (IFN-I) and interferon regulatory factor 7 (IRF7) at 24 and 36 h, respectively, as well as modulated IL-2, IL-8, and IL-10. Conversely, RNA interference-mediated knockdown of CiNFAT1 enhanced GCRV VP5 and VP7 mRNA levels and suppressed IL-2 and IL-8 expression. These results suggest that CiNFAT1 contributes to anti-GCRV immunity by promoting antiviral and inflammatory cytokine responses, thereby inhibiting viral replication. This study provides a foundational understanding of the NFAT genetic family in grass carp and highlights an important role of CiNFAT1 in mediating the body’s inherent defense mechanism against GCRV infection, offering insights for disease control strategies in aquaculture. Full article

In the early 1900s, eastern mosquitofish (Gambusia holbrooki) and western mosquitofish (Gambusia affinis) were deliberately and globally introduced for the biological control of mosquito larvae. Subsequently, both species developed a reputation for causing impacts on native small-bodied fish, amphibian larvae, and other aquatic species. This led to both species being considered some of the world’s worst invasive species. Due to morphological similarities, organizations worldwide often consider these species jointly when discussing their introduction and impacts. Recent studies suggest these species differ in fundamental ways, which could affect invasion success. Our goal was to compare eastern and western mosquitofish behavior and invasion success. Replicate populations were collected from the U.S. states of Florida (eastern mosquitofish) and Louisiana (western mosquitofish) to assess variation in aggression, boldness, and sociability. Mesocosm trials were used to compare invasion success between species following introduction to an ecosystem occupied by another small-bodied poeciliid. Eastern mosquitofish caused more damage to similar-sized heterospecifics and western mosquitofish exhibited greater boldness. No differences were found in sociability between the two species. In mesocosms, impacts were observed for both mosquitofish species but were greatest for heterospecifics with eastern mosquitofish. This suggests that two invasive species, even with similar life history and morphology, can differ in traits related to invasion success and ecological impacts. It is important to correctly identify mosquitofish species when evaluating their invasion. Full article

In crab pond environments, obstacles such as long aerobic pipelines, aerators, and ground cages are usually sparsely distributed. Automatic feeding boats can navigate while avoiding obstacles and execute feeding tasks along planned paths, thus improving feeding quality and operational efficiency. In large-scale crab pond farming, a single feeding operation often fails to achieve the complete coverage of the bait casting task due to the limited boat load. Therefore, this study proposes a multi-voyage path planning scheme for feeding boats. Firstly, a complete coverage path planning algorithm is proposed based on an improved genetic algorithm to achieve the complete coverage of the bait casting task. Secondly, to address the issue of an insufficient bait loading capacity in complete coverage operations, which requires the feeding boat to return to the loading wharf several times to replenish bait, a multi-voyage path planning algorithm is proposed. The return point of the feeding operation is predicted by the algorithm. Subsequently, the improved Q-Learning algorithm (I-QLA) is proposed to plan the optimal multi-voyage return paths by increasing the exploration of the diagonal direction, refining the reward mechanism and dynamically adjusting the exploration rate. The simulation results show that compared with the traditional genetic algorithm, the repetition rate, path length, and the number of 90° turns of the complete coverage path planned by the improved genetic algorithm are reduced by 59.62%, 1.27%, and 28%, respectively. Compared with the traditional Q-Learning algorithm, average path length, average number of turns, average training time, and average number of iterations planned by the I-QLA are reduced by 20.84%, 74.19%, 48.27%, and 45.08%, respectively. The crab pond experimental results show that compared with the Q-Learning algorithm, the path length, turning times, and energy consumption of the I-QLA algorithm are reduced by 29.7%, 77.8%, and 39.6%, respectively. This multi-voyage method enables efficient, low-energy, and precise feeding for crab farming. Full article

Temperate streams are among the most well-studied ecosystems globally, yet there remains much uncertainty regarding the processes that regulate food web structure. Here we explore the relative contribution of food web composition and watershed factors on inter-stream variation in size spectra slopes (λ). Size spectra describe the decrease in abundance with increasing body size of individuals within a community (N∼M ^λ). We estimated λ for invertebrate, fish, and combined food webs to test effects of functional groups and watershed variables. The mean λ for combined and invertebrate food webs aligned well with theoretic predictions (mean = −2.04 and −2.02 respectively, range =−2.58 to −1.51). In contrast, the mean fish slope was shallower and more variable among sites (mean = −1.85, range = −2.71 to −1.33). Drainage area, a proxy for ecosystem size, was positively related to λ in all three data groupings. The fish-only λs were also positively related to agricultural land cover and negatively associated with the relative abundance of predators and omnivores. These results demonstrate the potential for drainage area to increase the relative abundance of large consumers and highlight the role of functional group dominance. Such insights are difficult to obtain without a size spectrum approach. Full article

The Yuanjiang River, situated in the upper reaches of the Red River, is a crucial component of a biodiversity hotspot in the mountains of southwestern China, supporting a high diversity of fish species. Nevertheless, systematic research on fish diversity in the Yuanjiang River is scarce, scattered, and outdated. In our study, we produced 764 DNA barcodes belonging to 64 fish morphospecies to evaluate fish diversity in the Yuanjiang River. Barcoding gap analysis and DNA-based delimitation approaches achieved a high identification success rate (>93%), indicating that DNA barcoding is a practical approach for delimiting fish in the Yuanjiang River. However, four species were characterized by high levels of intraspecific divergence, generating multiple clades and/or molecular operational taxonomic units (MOTUs), suggesting that these species might comprise undetected species. Meanwhile, two closely related species within the genus Schistura, i.e., S. callichroma and S. caudofurca, cannot be delimited by the DNA barcoding technique, which is indicative of recent speciation. In summary, this study established a reliable DNA barcode reference library for fish species in the Yuanjiang River and revealed previously unknown fish diversity. Full article

Yellowfin tuna (Thunnus albacares) constitutes a critical global fishery resource, and its distribution pattern is correlated to varying degrees with the marine environment. This study utilized longline fishing data from the Western and Central Pacific Fisheries Commission (WCPFC) and the Inter-American Tropical Tuna Commission (IATTC) spanning 2004 to 2020, categorized by quarter and combined with surface and 0–200 m depth environmental variables. Geographical random forests (GRF) were employed to examine spatially non-stationary relationships between yellowfin tuna resources and environmental factors. Additionally, by integrating GRF with GeoShapley explainable methods, we quantitatively evaluated the mechanistic impacts of environmental drivers on tuna distribution across spatial scales. The findings indicated that (1) the GRF model demonstrated superior performance throughout all four quarters, with the goodness of fit on the 20% test set (R² = 0.72–0.85) consistently surpassing that of conventional random forest (RF) (R² = 0.68–0.79) and extreme gradient boosting random forest (XGBRF) (R² = 0.68–0.80). Moreover, in most cases, it had a lower RMSE and MAE, while effectively addressing spatial heterogeneity issues in yellowfin tuna fishery resources across most regions. (2) GeoShapley spatial explainable analysis revealed distinct environmental drivers, showing that the sea surface temperature and temperature at 105 m depth significantly influenced yellowfin tuna resources across all quarters, following a “high-value promotion, low-value inhibition” pattern, with salinity and dissolved oxygen at 105 m depth in Q2–Q3 and mixed-layer depth in Q3 also demonstrating notable effects. (3) Significant spatiotemporal heterogeneity was observed. The main spatial effects and temperature–depth–locality interactions remained significant throughout the year; mixed-layer depth–locality interactions were prominent in Q1, Q3, and Q4, dissolved oxygen–locality interactions in Q2 and Q4, and 105 m salinity–locality interactions exclusively in Q2. This study used geographical random forests (GRF) to integrate spatial statistics and machine learning to model the relationship between Pacific yellowfin tuna fishery resources and environmental factors. This approach demonstrates potential in improving spatial predictions of heterogeneous tuna resources and may help to identify key environmental drivers influencing their distribution. These findings provide essential insights for the formulation of science-based management strategies for Pacific yellowfin tuna fisheries. Full article

The European seabass is a key Mediterranean aquaculture species, vital for sustainably meeting rising global protein demands amid declining wild fish stocks. Genetic analyses have identified the six6 gene as a candidate target of domestication and selective breeding, with two SNPs showing significant genotypic differences between wild and farmed European seabass populations. Further analyses revealed differential six6 expression between larval and juvenile stages, suggesting a potential developmental role. This study explores associations between these SNPs and important aquaculture traits across early developmental stages. Seabass samples were examined at 34 days post-hatching (dph, larval stage) and 71 dph (juvenile stage). We examined associations between specific six6 SNPs and morphological traits using traditional morphometrics, analyzing 20 and 26 characteristics in the larval and juvenile stages, respectively. Shape and size differences were examined with allometric correction. The six6 gene was primarily associated with body length, height, and caudal fin morphology. Notably, homozygous six6 genotype combinations at the studied SNPs were associated with increased body length in a developmental stage-specific manner. Variation in this gene also appeared to influence eye development in juveniles. These findings offer phenotypic evidence supporting previous genetic and expression studies in European seabass, highlighting their potential applications in fisheries and aquaculture. Full article

Vertical slot fishways are a crucial measure to mitigate the blockage of fish migration caused by hydraulic engineering infrastructures, but their passage efficiency is often hindered by the complex interactions between fish behavior and hydrodynamic conditions. This study combines computational fluid dynamics (CFD) simulations with behavioral laboratory experiments to identify the hydrodynamic characteristics and swimming strategies of three types of fishways—Central Orifice Vertical Slot (COVS), Standard Vertical Slot (SVS), and L-shaped Vertical Slot (LVS)—using the endangered species Schizothorax prenanti from the upper Yangtze River as the study subject. The results revealed that (1) a symmetric and stable flow field was formed in the COVS structure, yet the passage ratio was the lowest (50%); in the SVS structure, high turbulent kinetic energy (peak of 0.03 m²/s²) was generated, leading to a significant increase in the fish’s tail-beat angle and amplitude (p < 0.01), with the passage time extending to 10.2 s. (2) The LVS structure induced a controlled vortex formation and created a reflux zone with low turbulent kinetic energy, facilitating a “wait-and-surge” strategy, which resulted in the highest passage ratio (70%) and the shortest passage time (6.1 s). (3) Correlation analysis revealed that flow velocity was significantly positively correlated with absolute swimming speed (r = 0.80), turbulent kinetic energy, and tail-beat parameters (r > 0.68). The LVS structure achieved the highest passage ratio and shortest transit time for Schizothorax prenanti, demonstrating its superior functionality for upstream migration. This design balances hydrodynamic complexity with low-turbulence refuge zones, providing a practical solution for eco-friendly fishways. Full article

In this study, the growth and welfare of the African catfish (Clarias gariepinus, Burchell 1822) were investigated under industrial farming conditions. For this purpose, the growing success (cm, g) and typical stress related parameters (glucose-, lactate-, cortisol-concentrations, growth hormone, HSI-liver index) were investigated on the African catfish (102–841 g) in relation to an external stressor (working light and noise) and different feeding regimes (day, night, and day and night feeding) over 83 days. As no significant effects were found among the experimental feeding treatments in relation to the growth performance and investigated stress parameters, the time of feeding seems to have less impact to the production success and stress reactions as suggested before. Regarding our results, the effect of feeding conditioning could have played a strong factor likewise the ageing process of the reared fish species which is known to be rather photophobic. Therefore, the factor of conditioning and its influence to the time shift in feeding regimes and the impact of noise and light stressors during feeding should be investigated separately in future experiments to obtain further results in this context and clarify the validity of the best feeding conditions for African catfish. Full article

The oriental river prawn (Macrobrachium nipponense) is one of the most popular freshwater prawn in China. In order to study the relationships between morphometric traits and body mass across different geographical locations and provide references of phenotypic traits for the breeding of M. nipponense, we collected wild M. nipponense from three locations (main stream, HH; Suyahu Reservoir, SYH; and Wuyue Reservoir, WY) in the upper reaches of the Huaihe River, China, and measured 26 morphometric traits and body masses. We found that the coefficient of variation of body mass varied from 31.88% to 59.27% across the three populations, exceeding that of morphometric traits within each population. All 26 morphometric traits, except for the fourth abdominals somite length in the WY population, were observed to correlate significantly positively with body mass (p < 0.05). A path analysis indicated that propodus length, body length, ischium length, carapace height, and second abdominals somite length in the HH population; body length, propodus length, abdominal height, sixth abdominals somite length, and telson length in the SYH population; and body length, carapace height, fifth abdominals somite length, and abdominal height in the WY population significantly affected body mass directly (p < 0.05). Comparing the pathway analysis with the grey relation analysis, we can conclude that the trait most correlated with body mass was body length across the three geographical populations. These findings provide references of waiting morphological traits for M. nipponense selective breeding in different geographical populations. Full article

Ammonia is widely regarded as the primary chemical pollutant responsible for fish toxicity in aquaculture. Scatophagus argus is an economically important euryhaline species extensively cultured in marine aquaculture. To investigate its physiological responses and molecular mechanisms under ammonia exposure, we determined the 96 h median lethal concentration (LC₅₀-96 h) of total ammonia nitrogen (TAN) for S. argus juveniles. Histopathological analyses were conducted at TAN concentrations of 0 (control), 30, and 60 mg/L, with transcriptomic analysis performed at 0 and 60 mg/L. The results showed that the LC₅₀-96 h for S. argus was 59.43 mg/L. Histological analysis revealed lamellar epithelial detachment and hepatocyte vacuolization in S. argus exposed to 60 mg/L TAN, indicating substantial structural impairment under ammonia stress. Transcriptomic profiling identified 245 differentially expressed genes (DEGs), comprising 142 upregulated and 103 downregulated genes. KEGG enrichment analysis indicated that DEGs were primarily enriched in energy metabolism and immune-related pathways. Key genes involved in glucose metabolism, amino acid metabolism, and cellular regulation (e.g., PFKM, PGM1, MAT2A, DDIT4) were significantly upregulated in energy metabolism pathways. In immune-related pathways, immune regulatory genes such as GIMAP4 and ARRDC3 were upregulated, while NAMLAA, associated with inflammatory modulation, was downregulated. Collectively, these transcriptional changes suggest that S. argus responds to external ammonia stress through coordinated regulation of energy metabolism and immune function. This study provides novel insights into the physiological and molecular strategies employed by S. argus in response to ammonia toxicity, offering a reference for environmental risk assessment and aquaculture management. Full article

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

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

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

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

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

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

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