To investigate the effects of photoperiod on the feeding rhythms and gastrointestinal evacuation dynamics of second-instar juvenile Tachypleus tridentatus, this study examined diel feeding rhythms in second-instar juvenile T. tridentatus using eight observation time points over 24h under three photoperiod regimes: natural photoperiod, constant light, and constant darkness. Feeding rhythms were assessed via gastrointestinal satiety indices, and evacuation dynamics were tracked for 24h after satiation. The results showed that there were no significant differences in average satiety among time points within any photoperiod at 3h or 6h post-feeding. Under natural photoperiod at 3h, satiety was significantly higher at night than during the day, whereas no clear diel differences were observed under continuous light or darkness. By contrast, at 6h post-feeding, satiety indices were consistently higher at night than during the day under all three photoperiods. Feeding peaks under the natural photoperiod at 3h post-feeding occurred during the night-time period (21:00—06:00), while no distinct diel feeding rhythm was detected under continuous light or darkness. However, at 6h post-feeding, clear feeding rhythms emerged under both continuous light and continuous darkness, with feeding peaks occurring at 21:00—09:00, and 21:00—06:00, respectively. Most juveniles achieved substantial food intake within 3h, with only marginal increases observed by 6h. Gastrointestinal evacuation exhibited a biphasic pattern characterized by an initial rapid phase followed by a slower phase. First-time feeding juveniles reached 50% evacuation at 14.7h and 80% at 27.1h after satiation, whereas non-first-time feeding juveniles reached the same benchmarks at 8.8h and 16.3h, respectively. These findings demonstrate that second-instar juvenile T. tridentatus exhibit a pronounced diel feeding rhythm, only weakly influenced by photoperiod. Based on these results, it is recommended that juvenile rearing be conducted under a natural photoperiod with at least one feeding event after dusk and moderately extended during the early feeding stage. This study provides a scientific basis for optimizing feeding strategies in the artificial culture of juvenile T. tridentatus.

The efficient underwater sensing and attack mechanisms of electric eels provide significant inspiration for the development of biomimetic equipment. To this end, this paper investigates the response strategies and discharge patterns of electric eels under various behavioral intents. By constructing specialized test scenarios and integrating behavioral recordings, data acquisition, and bio-electric field simulations, we systematically analyzed the correlation between attack/defense postures and discharge logic, as well as the corresponding discharge characteristics of electric organs. The results reveal that a curled attack posture enhances targeting efficiency through synergistic electric field and circuit interactions. Simulations indicate it can increase the voltage delivered to prey more than three times. Touch-based experiments further identified a deep-water passive defense mechanism through double/triple pulses. By comparing behavioral and electrogenic organ discharge (EOD) patterns in active and passive defense, this study concludes that active defense is suitable for shallow water, while passive defense is suitable for deep water environments, providing a more complete theoretical framework for understanding the different biological behaviors in electric eels.

To investigate the impact of the ten-year fishing ban on fish community structure and diversity, this study conducted fish resource surveys in four sections of the middle Yangtze River—Zhijiang, Jianli, Yueyang, and Huangshi—during the spring and autumn seasons from 2022 to 2024. A total of 91 species belonging to 15 families and 10 orders of fish were investigated. Cyprinidae fish are the most abundant (59 species, 64.84%), with lake-type fish (47.25%) and omnivorous fish (65.93%) being the predominant ecological types. Relative Importance Index (IRI) analysis identified eight dominant species: silver carp, bighead carp, crucian carp, grass carp, silver bream, snakehead, shortjaw goby, and yellow catfish, predominantly medium-to-large economic fish. In 2024, 72 fish species were monitored in the middle reaches of the Yangtze River, representing an increase of 10 species compared to 2022, while the average catch per unit effort (CPUE) rose by 11.35% to 10.40 kg per haul. The Shannon-Wiener diversity index remained relatively stable (3.06—3.22). The abundance/biomass comparison curve indicated low disturbance in the fish communities. Cluster and NMDS analyses separated the fish community into two distinct clusters: Zhijiang formed one cluster, while Jianli, Yueyang, and Huangshi formed another. Following the implementation of the 10-year fishing ban in the Yangtze River, CPUE showed an upward trend. Key fish resources such as the four major carp species and croaker recovered relatively quickly, indicating phased success of the ban. However, the diversity index remained relatively stable, suggesting that species diversity recovery is a long-term process. These findings provide scientific support for evaluating the effectiveness of the fishing ban and dynamically adjusting related policies.

To investigate the synergistic effects of probiotics and microalgae on larval rearing performance of giant freshwater prawn (Macrobrachium rosenbergii), this study selected Haematococcus pluvialis and Oocystis borgei, which were respectively combined with Clostridium butyricum and Lactobacillus for treatment. The impacts of different probiotic-microalgal combinations on larval survival, growth, development, water quality, and physiological parameters were systematically evaluated. The results showed that the O. borgei+Lactobacillus treatment achieved the highest survival rate (85.80%), significantly higher than that of the control group (50.2%, P<0.05), while the O. borgei+C. butyricum combination exhibited optimal performance in promoting larval growth and development. The two microalgae species demonstrated functional differentiation in water quality regulation: H. pluvialis showed significant advantages in nitrogen removal, whereas O. borgei was most effective in reducing organic matter load (COD_cr). Physiological analysis showed that probiotic-microalgal combinations could effectively alleviate oxidative stress in larvae, with malondialdehyde (MDA) content reduced by 68.3%—87.3% compared to the control (P<0.05), among which the H. pluvialis+C. butyricum combination demonstrated the strongest overall performance in antioxidant, immune, and digestive functions. Stepwise regression analysis revealed that total inorganic nitrogen (TIN) concentration and MDA were the key driving factors affecting larval survival rate, jointly explaining 61.0% of the variation. This study elucidates the mechanism by which probiotic-microalgal synergy enhances larval rearing efficiency through nutrient cycling and physiological regulation, providing theoretical basis and technical reference for microecological intervention in crustacean larviculture.

To understand the diversity characteristics and interannual variations of the fish community in the middle reaches and tributaries of the Huishui River during the early stage of the fishing ban, fish resource surveys were conducted from 2021 to 2023. A total of 59 fish species were collected, belonging to 40 genera, 12 families, and 7 orders. Among them, Cyprinidae fish were in an absolute dominant position, accounting for 67.80% of the total species, 89.22% of total abundance, and 91.65% of total biomass. The ecological types are dominated by benthic, omnivorous, and spawn-laying fish, with the proportions of species being 55.93%, 55.93%, and 44.07% respectively. Interannual characteristics showed that species richness ranged from 35 to 49, among which the common dominant species were Zacco platypus and Acrossocheilus fasciatus. The Margalef index, Shannon-Wiener index, and Pielou index all showed a fluctuating upward trend overall, ranging from 4.18—5.34, 1.97—2.37, and 0.55—0.62, respectively, while the Simpson index showed a downward trend from 0.19 to 0.31. Cluster analysis showed that community structure in spring, summer, and winter of 2021 was similar, as was that in winter of 2022 and winter of 2023; all other sampling occasions grouped together. This suggests that community recovery followed distinct phases, with a unique response pattern in the early stage (2021). Spatially, the main stream and tributaries generally formed separate clusters, indicating that habitat-driven differences remained dominant. Overall, the recovery of community structure was driven by multiple factors under temporal dynamics, including habitat conditions and seasonal variation, exhibiting phased progression and spatial heterogeneity. This research clarifies the characteristics and diversity trends of the fish community in the Huishui River during the initial stage of the fishing ban, providing a basis for the assessment of the fishing ban effect and the scientific management of aquatic biological resources.

The functional restoration of large river ecosystems represents a significant global challenge. The “Ten-Year Fishing Ban” implemented across the Yangtze River Basin, a large-scale ecological intervention, offers an unprecedented opportunity to investigate the recovery processes in a highly regulated aquatic ecosystem. This study aimed to comprehensively explore structural changes in the fish community food web in the tailrace of the Three Gorges Reservoir (TGR) after the fishing ban. We focused on two hydro-morphologically distinct river sections, the downstream Fuling section and the upstream Mudong section, to analyze the spatio-temporal responses of the food web. Our methodology integrated stable isotope analysis (δ¹³C and δ¹⁵N), an advanced Bayesian Isotope Mixing Model (BIMM) incorporating trophic-level constraints and prior dietary information, and food web topological analysis. Fish and basal food source samples were collected before (2018—2019) and after (2023) the ban implementation. Our results reveal that although species richness recovered similarly in both sections (increasing to 36 species each), food web restructuring followed two divergent pathways shaped by local habitat. The food web exhibited “vertical deepening”: connectance decreased from 0.085 to 0.070 and generalization index from 2.55 to 2.44, indicating more specialized trophic interactions. Concurrently, an expanded δ¹⁵N range (10.94‰ to 11.51‰) reflected food chain elongation, and the proportion of omnivorous species rose from 58.3% to 65.5%. These shifts, together with an increased piscivorous diet in the key predator Siniperca kneri, support a top-down recovery cascade driven by restored predator populations. In contrast, the riverine Mudong section underwent “bottom-up reorganization” toward a flatter structure: connectance increased from 0.070 to 0.077 and the generalization index from 2.21 to 2.69, suggesting more generalized feeding links. However, this was accompanied by a compressed δ¹⁵N range (11.77‰ to 10.47‰), indicating a shorter food chain, and a decline in omnivory from 65.4% to 55.2%. Isotopic data revealed greater reliance on terrestrial C3 plant-derived carbon sources. The diet of the key predator, Culter alburnus, shifted from 78.9% to 64.9%, reflecting increased use of lower-trophic-level resources. This pattern suggests that the recovery was primarily driven by enhanced primary production and terrestrial organic matter inputs, facilitated by stronger land-water coupling and Flood Pulse Concept. In conclusion, ecological recovery after a major conservation intervention such as the fishing ban is not uniform; trajectory depends on local environmental conditions such as flow velocity and floodplain connectivity. These findings underscore the critical importance of assessing functional attributes like food web structure alongside biodiversity metrics. This research provides a crucial scientific foundation for developing and implementing spatially differentiated, adaptive management in the Yangtze River Basin to improve the effectiveness of large-scale conservation efforts.

Polycyclic aromatic hydrocarbons (PAHs), as a class of persistent organic pollutants (POPs), tend to accumulate in organisms due to their lipophilic. Penaeus vannamei, widely cultivated in such settings, is particularly susceptible to PAHs contamination, which may ultimately endanger human health. In this study, the contamination characteristics, ecological risks, and human health risks of 16 PAHs in a cultured water-biological system were investigated. Results showed that the total concentrations of the 16 PAHs (∑PAHs) in aquaculture water ranged from 44.62 to 350.46 ng/L, with Nap, Phe, BaA, Pyr, Chr, Flu, and Ace being the main pollutants. Pollution source analysis based on characteristic ratios showed that PAHs originated primarily from oil, coal combustion, and other biomass combustion. In shrimp muscle, the total concentrations of 16 PAHs ranged from 0.34 to 208.37 μg/kg (dry weight, dw), with 12 PAHs detected, and LMW PAHs predominated, while 5- and 6-ring PAHs accounted for minor proportions. The ILCR values associated with dietary exposure to shrimp ranged from 1.08×10^–11—2.02×10^–8, which was much lower than the USEPA standard value of 1×10^–6, indicating negligible carcinogenic risk under current conditions.

The construction of the Guxian Water Control Project causes blockage of river sections, hindering population exchange between fish upstream and downstream across the dam. Fish passage facilities can mitigate this barrier, and detailed knowledge of fish swimming behavior is critical for their effective design. This study targeted two main fish species for the project: Leuciscus waleckii Dybowski and Opsariichthys bidens-and tested their induced velocity and critical swimming speed. The study also analyzed ecological behavioral indicators including tail-beat frequency, tail-beat amplitude, body wave velocity, body wave length, maximum head angle, and maximum head angle velocity during upstream swimming at three swimming velocitys (2, 4, and 6 BL/s). The results showed that the absolute induced velocities of Leuciscus waleckii Dybowski and Opsariichthys bidens were (0.06±0.01) and (0.11±0.03) m/s, respectively, with corresponding relative values of (0.55±0.11) and (1.11±0.27) BL/s. The absolute and relative rheoreaction velocities of Leuciscus waleckii both exhibited significant negative correlations with body length (P<0.05), whereas the absolute rheoreaction velocity of Opsariichthys bidens showed a significant positive correlation with body length (P<0.05). The absolute critical swimming speeds of Leuciscus waleckii Dybowski and Opsariichthys bidens were (0.99±0.20) and (0.96±0.14) m/s, respectively, and the relative critical swimming speeds were (9.30±1.14) and (10.07±1.47) BL/s, respectively. Both absolute and relative critical swimming speeds of Leuciscus waleckii Dybowski were significantly positively correlated with body length (P<0.05). For both species, tail-beat frequency, body wave velocity, and maximum head angle velocity increased with flow velocity, while tail-beat amplitude and maximum head angle decreased with increasing flow velocity. The body wave length of Leuciscus waleckii Dybowski at 2 BL/s was significantly higher than that under the other two swimming velocitys (P<0.05), whereas the body wave length of Opsariichthys bidens showed no significant change with increasing flow velocity (P>0.05). Among the ecological behavioral indicators, tail-beat frequency, maximum head angle velocity, and body wave velocity showed the strongest correlations with swimming speed, suggesting their central role in propulsion. For fish-passage designs targeting Leuciscus waleckii Dybowski and Opsariichthys bidens, we recommended an entrance velocity of 0.9—1.2 m/s for upstream collection vessels and an internal velocity of 0.1—0.9 m/s within the collection chamber. This study quantifies the swimming ability and key swimming behavioral characteristics of two representative fish-passage target species, providing a reference for the design and optimization of fish passage facilities.

To investigate the relationship between personality traits and cognitive abilities in fish, this study used juvenile Chindongo demasoni, a highly social cichlid species, as the model organism. Through associative learning training and tests based on a “color-food reward” paradigm, we assessed cognitive performance and analyzed its correlation with three personality traits: activity, boldness, and sociability. The results showed that: (1) Activity and boldness were positively correlated in Chindongo demasoni (P=0.024), supporting the Behavioral Syndromes Hypothesis; (2) The fish successfully formed associations between color cues and food rewards through associative learning, with the correct choice rate increasing significantly over training days (P<0.001); (3) Sociability was positively correlated with cognitive performance, as measured by the correct choice rate during the test phase (P=0.006), while no significant relationship was found between cognitive performance and either activity or boldness. The link between sociability and cognitive ability supports the Social Brain Hypothesis, suggesting that for social fish, the demand to process complex social information may be an important driver in the evolution of cognition.

To explore the influence of nutrient sources on the beta diversity patterns of macrozoobenthic communities in plateau lakes, a quantitative survey of macrozoobenthos and their nutrient sources was conducted in the Zhaling Lake and Eling Lake basins from 2022 to 2024 in the dry and wet seasons. A total of 108 taxa belonging to 8 orders, 39 families were collected. Overall, the lake, habitat, season, and their interactions showed no significant effects on zoobenthos species richness (P>0.05). However, total beta-diversity was relatively high and primarily driven by turnover component. We used parameters in water (chlorophyll a, phytoplankton, total nitrogen, total phosphorus) and catchment characteristics (vegetation coverage, altitude differences, precipitation) to quantify allochthonous inputs and autochthonous nutrients. The Chl.a was significantly higher in the wet season than that in the dry season (P<0.001), and the allochthonous input in the littoral zone of Eling Lake was significantly higher than that in the river region (P<0.01). The Random Forest model indicated that allochthonous nutrient had a stronger correlation with the beta-diversity of the macrozoobenthic community. Allochthonous inputs outweighed autochthonous nutrients in both river and littoral zones during the wet season. In contrast, during the dry season in littoral zone, the importance of autochthonous nutrients such as chlorophyll a and total phosphorus increased significantly, revealing a co-dominant pattern driven by internal and external sources. The total beta diversity and its turnover component exhibited greater sensitivity to allochthonous input, while nestedness in river zone during the wet season also showed certain responsiveness to autochthonous nutrient. These findings provide fundamental scientific support for the ecological management of plateau lake ecosystems.