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 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.

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 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.

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.

To investigate interspecific variations in group behaviour characteristics among six Cyprinidae species and their responses to exercise training, we selected Carassius auratus, Tinca tinca, Cyprinus carpio, Spinibarbus sinensis, Procypris rabaudi, and Acrossocheilus fasciatus as experimental subjects. At 25℃, each species was divided into control groups, anaerobic exercise training groups (1 session/d), and aerobic exercise training groups [4 times body length per second (bl/s), 18h/d] for three weeks. Subsequently, within a six-arm maze, the following parameters were measured under both non-predator and simulated predator stimuli: centre density (CD), shelter density (SD), non-shelter density (NSD), and cohesion index (I_c). The results indicated that under both non-predator and simulated predator stimulation, the control groups of C. auratus, T. tinca, C. carpio, and S. sinensis exhibited relatively higher CD, NSD, and I_c values along with lower SD, whereas the control group of P. rabaudi showed relatively lower CD and NSD along with I_c higher SD and I_c values. The control group of A. fasciatus displayed relatively lower CD, SD, and I_c values but higher NSD. Regardless of predator stimulation, exercise training did not produce statistically significant effects on the collective behavioral characteristics of C. auratus, T. tinca, and C. carpio. Anaerobic exercise training led to an 81% significant decrease in NSD and a 21% significant increase in I_c values in P. rabaudi under non-predator stimulation (P<0.05); anaerobic exercise training resulted in a 39% significant increase in I_c values in A. fasciatus under simulated predator stimulation (P<0.05); aerobic exercise training caused a 17% significant decrease in I_c values in S. sinensis under non-predator stimulation (P<0.05). The study demonstrates that: (1) There are significant interspecific differences in the collective behavioral characteristics among the six cyprinid species, which may be related to their living habits and habitat factors; (2) Exercise training exerts varying degrees on collective behavioral characteristics by fish species and training regimen.

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.

This study used the Soil and Water Assessment Tool (SWAT) to simulate the transport and export of butachlor, a typical herbicide, under agricultural non-point source pollution conditions in the Caizi Lake basin. Model calibration and validation indicated satisfactory simulation performance. The results revealed pronounced spatiotemporal variation in butachlor export. Temporally, 79.32% of the annual butachlor load occurred between June and July, closely associated with intensive rainfall and increased runoff following herbicide application in May–June. Daily butachlor export was significantly and positively correlated with daily runoff (P<0.01, r=0.632). Interannual differences were also evident, with export loads in wet years (e.g., 2016) substantially exceeding those in dry years (e.g., 2018). Spatially, the lower sub-watersheds (sub-basins 13, 17, and 19) were identified as primary export zones, with markedly higher outputs than upstream areas. Among land use types, water bodies had a significant effect on butachlor export, whereas cropland and forestland showed relatively weak impacts, highlighting the retention and transmission function of pond networks in multi-pond systems. These findings provide a scientific basis for managing agricultural non-point source pollution and pesticide use in the Caizi Lake basin, with important implications for safeguarding watershed water quality and optimizing regional agrochemical strategies.

As a crucial in-situ remediation technology for river and lake water bodies, ecological enclosure technology effectively inhibits pollutant diffusion, improves the aquatic environment, and enhances stability of river and lake ecosystems through multiple mechanisms such as physical isolation, chemical regulation, and biological enhancement. This paper reviews the operational mechanisms, types, and application effects of ecological enclosure technology in the ecological restoration and protection of rivers and lakes. Building on current literature, we identify existing limitations and propose future directions for both basic research and engineering applications. Future development should prioritize novel materials and technologies for key enclosure components while optimizing construction methods to ensure long-term stability and effectiveness. In addition, systematic numerical simulation methods should be incorporated to predict enclosure durability and ecological impacts, supporting the evolution of enclosure structures towards modularization and intelligence. Ultimately, the comprehensive performance of ecological enclosures should be improved under the premise of reducing management and operation costs and minimizing ecological risks. This study not only provides theoretical support for enhancing the stability and functionality of ecological enclosure technology but also offers technical references for professionals in the aquatic ecological restoration industry. It is expected to promote the sustainable application of this technology.