This study evaluated the habitat coloration preferences of Siniperca chuatsi and Cirrhinus molitorella in both solitary (n = 1) and group (n = 3) settings across six colors. The results indicated that both individual and group S. chuatsi spent the majority of their time in and made frequent visits to the black area, followed by the blue area. While individual C. molitorella spent the majority of their time and visits in the blue region, groups showed a preference for the blue and white regions. These findings highlight the distinct habitat coloration preferences of S. chuatsi and C. molitorella in different group states, suggesting that habitat coloration has an important effect on fish behavior and environmental adaptation. From a behavioral ecology perspective, these preferences may be closely related to the survival strategies of fish. Notably, C. molitorella’s strong preference for blue and white backgrounds may reflect anti-predator behavior, helping C. molitorella avoid predators, such as S. chuatsi, in natural environments, thereby improving its chances of survival. This study provides a scientific basis for optimizing aquaculture environments, emphasizing the importance of considering habitat coloration and substrate type in designing environments to enhance fish welfare.

Understanding spatiotemporal patterns of fish density and their environmental drivers is critical for managing river–lake ecosystems, yet dynamic interactions in heterogeneous habitats remain poorly quantified. This study combined hydroacoustic surveys, spatial autocorrelation analysis (Moran’s I), and generalized additive models (GAMs) to investigate seasonal and spatial fish distribution, aggregation characteristics, and regulatory mechanisms in China’s Zhelin Reservoir. The results reveal pronounced seasonal fluctuations, with summer fish density peaking at 13.70 ± 0.91 ind./1000 m³ and declining to 1.95 ± 0.13 ind./1000 m³ in winter. Spatial heterogeneity was evident, with the Xiuhe region sustaining the highest density (15.69 ± 1.09 ind./1000 m³) and persistent hotspots in upstream bays. Transient high-density clusters (90–99% confidence) near the Zhelin Dam during summer suggested thermal or hydrodynamic disturbances. GAM analysis (R²adj = 0.712, 78.5% deviance explained) identified seasonal transitions (12.26% variance), water depth (16.54%), conductivity (13.75%), and dissolved oxygen (13.29%) as dominant drivers, with nonlinear responses to depth and bimodal patterns for conductivity/oxygen. These findings demonstrate that hydrological seasonality and habitat heterogeneity jointly govern fish aggregation, underscoring the ecological priority of Xiuhe and upstream bays as core habitats. This study provides a mechanistic framework for guiding reservoir management, including targeted conservation, dam operation adjustments to mitigate hydrodynamic impacts, and integrated strategies for balancing hydrological and ecological needs in similar ecosystems.

The Geheyan Reservoir, located on the Qingjiang River, a tributary of the Yangtze River, is important for regional water supplies and ecological conservation. Understanding changes in ecosystem structure and function has become critical for assessing efficacy after the implementation of a fishing ban. This study employs the Ecopath model to examine the ecosystem characteristics of the Geheyan Reservoir before (2017) and after (2022) the fishing ban. The results show significant differences in trophic levels, energy transfer efficiency, and ecosystem maturity between the two periods. The trophic levels increased from 3.36 pre-fishing ban to 3.89 post-ban, indicating an enhanced complexity in the food web structure. The highest eco-trophic efficiency for major commercial fish species increased after the ban, indicating improved energy utilization efficiency. However, energy transfer bottlenecks were still observed between trophic levels II and IV, suggesting ongoing challenges in nutrient cycling. The total primary production-to-total respiration ratio (6.93) and the connectivity index (0.25) indicate that the ecosystem’s maturity and stability have improved after the fishing ban. These findings underscore the ban’s effectiveness and provide a scientific foundation for sustainable management of Geheyan Reservoir and similar ecosystems in the Yangtze River Basin.

Coreius guichenoti, an endemic fish of the upper Yangtze River, has experienced severe population decline due to overfishing and habitat fragmentation. To inform its conservation, this study compared life-history traits between artificially bred and historical wild populations, revealing pronounced plasticity in response to environmental conditions. The cultured population, dominated by age 0–4 individuals but retaining a notable proportion of age 5–6 fish, exhibited faster growth and higher fecundity (mean absolute fecundity 32,724 ± 24,132 eggs; relative fecundity 37.5 ± 18.5 eggs/g) than the wild population. In contrast, the wild group consisted of >90% age 0–4 individuals, showed virtually no fish aged 5–7, reproduced seasonally with high total egg output, and tended toward a periodic life-history strategy, whereas the cultured group tended toward an opportunistic strategy that still retained some periodic traits. These results demonstrate that C. guichenoti can adjust its life history on a within-generation scale. Accordingly, we recommend pre-release conditioning with moderate flow and temperature variations to enhance field adaptability. This study provides evidence-based guidance for broodstock selection and preconditioning in restocking programs, aimed at improving post-release survival and reproductive success in the wild.

Rearing space is a critical environmental factor influencing fish behavior and welfare. However, the effects of rearing space scale on group spatial structure and physiological stress under constant stocking density remain poorly understood. This study used juvenile largefin longbarbel catfish (Hemibagrus macropterus) as the experimental subject. Three circular rearing tanks with diameters of 0.8, 1.5 and 2.0 m were established at the same stocking density (160 individuals/m³). A computer visionbased behavioral analysis pipeline integrating SAM3 and YOLO11 was applied to quantify group nearest neighbor distance (NND), Clark–Evans index (R value), convex hull aggregation index, swimming speed, directional consistency, sidewall intensity and behavioral states. Serum cortisol, 5hydroxytryptamine (5HT) and dopamine (DA) concentrations were also measured to assess the effects of rearing space scale on group spatial structure, locomotor behavior and physiological stress.,Under constant stocking density, rearing space scale significantly altered group spatial structure and physiological indicators of H. macropterus. As tank diameter increased, mean NND increased while the Clark–Evans R value decreased, indicating that absolute interindividual distance increased, whereas the group exhibited a stronger tendency toward aggregation relative to the available space. Mean swimming speed increased and sidewall intensity decreased with increasing tank size, while directional consistency remained low across all treatments. Behavioral state analysis revealed that fish predominantly exhibited two states—active aggregation and active dispersion—with resting behavior consistently accounting for a negligible proportion. Cortisol responses showed clear spatial dependence: the 0.8 m group showed a continuous increase from 5 h to 5 d, indicative of chronic stress accumulation; the 1.5 m group reached the highest cortisol level during the acute phase, followed by a partial decline; and the 2.0 m group remained close to baseline at both time points, with no apparent stress response. 5HT concentration declined with increasing tank size, whereas DA showed no significant change.,Overall, the behavioral and physiological results demonstrate that rearing space scale significantly affects the group spatial structure, locomotor behavior and physiological stress state of H. macropterus under constant stocking density. Larger rearing space alleviates spatial confinement stress and provides more suitable conditions for maintaining good aquaculture welfare. This study provides a theoretical basis for optimizing rearing space in H. macropterus aquaculture and offers a reference for assessing rearing space suitability using behavioral and physiological indicators.