River–lake interaction is important for maintaining biodiversity, yet it is vulnerable to hydrological alteration. The connectivity of the channel connecting Poyang Lake and the Yangtze River not only ensures the regular migration of fish but also makes Poyang Lake a feeding and fattening ground for them. Unfortunately, human activities have dramatically changed the hydrodynamic conditions of Poyang Lake, which is experiencing severe drought due to the obvious decline in the water level in autumn and winter, especially since 2003. However, the possible impacts of the changes in the water level on the habitats of migratory fish remain unclear due to the limitation of traditional techniques in spatiotemporal analysis. Here, we combined a hydrodynamic model and habitat suitability model to simulate variations in the suitable habitat area and their connectivity under different water-level conditions. The conditions for the migration pathway of the target fish were obtained by a hydroacoustic survey using the Simrad EY60 echosounder. The results showed that the change in water level will significantly affect the spatiotemporal change in the suitable habitats and their connectivity. In particular, we found the existence of two thresholds that play a dominant role in illuminating the connectivity of effective suitable habitats (HC). Firstly, the maximum value of the weighted usable area (WUA) and HC can be achieved when the water level is more than 16 m. Secondly, when the water level is between 10 and 16 m, the changes in the HC are sensitive and rapid, and the area flooded at this stage is called the sensitive area. HC is a crucial element in fish migration and habitat conditions. Under the condition of continuous drought in the middle reaches of the Yangtze River, our research contributes to clarifying the influence of water level on key habitats for fish and optimizes the practice of river–lake ecological management.

A multi-mesh trammel net has been developed and used for sampling freshwater fishes. However, little is known about the catch efficiency of the net. This research investigated the catch efficiency of a multi-mesh trammel net (nominal mesh size; 10.0, 30.0, 50.0, and 70.0 mm) for fish sampling in the Yangtze River of China. Catch composition and factors affecting catch per unit effort based on fish number (CPUE_N), weight (CPUE_W), and species number (CPUE_S) were analyzed. The results showed that the net was capable of capturing a wide range of fish sizes (total length, 5.5 to 121.0 cm) and species (n = 50). Increasing soak time from 9.4 to 24.0 h resulted in a decrease in CPUE_N and CPUE_W while a longer soak time increased CPUE_S. CPUE_N, CPUE_W, and CPUE_S varied significantly with fishing locations. The net provides a potential complement to the current fish sampling techniques used in freshwater ecosystems (e.g., large rivers, lakes, and reservoirs). The findings of this research help to improve our understanding of the catch efficiency of the multi-mesh trammel net and provides insight into better designs for gears and methods for sampling diverse fish sizes and species.

This study provides a comprehensive analysis of the spatio-temporal dynamics of fish resources in the confluence waters of Poyang Lake and the Yangtze River, focusing on the initial phase of a 10-year fishing ban implemented in January 2020. Through hydroacoustic surveys conducted during both high-water (September 2020) and low-water (January 2021) periods, we identified significant variations in fish density and individual size across different sections. During the high water level period, fish concentrations were primarily observed in the confluence area between the Yangtze River and Poyang Lake, exhibiting higher densities compared to other regions. Conversely, fish congregated in the deep-water zones of the main river during the low water level period. The fish population was dominated by small to medium-sized individuals, with mean body lengths of 12.47 cm and 12.62 cm during the high and low water level periods, respectively. Notably, 42 and 33 fish species were recorded during the high-water and low-water surveys, respectively, emphasizing the region’s rich biodiversity. Importantly, the study demonstrates that the fishing ban has resulted in substantial increases in both fish density and mean body length, underscoring its effectiveness in fostering fish population recovery. These findings provide critical baseline data to inform scientific conservation and management strategies in this ecologically sensitive river–lake ecosystem.

Animal behavior diversity is a key element of biodiversity, and the establishment of an ethogram provides a crucial framework for exploring the relationship between behavioral patterns and environmental factors. However, the development of ethograms and the quantitative analysis of behavioral diversity in fish remain underexplored. In this study, focal animal sampling and instantaneous scan sampling methods, paired with the PAE (Posture-Act-Environment) coding system, were employed to investigate the ethogram and reproductive behavior diversity of silver carp. The findings revealed 12 postures, 20 actions, and 34 behaviors documented during the breeding period of silver carp. Analysis of reproductive behavior diversity revealed that the absolute behavioral diversity index (H), relative behavioral diversity index (r), and regulated diversity index (r-variable) all peaked during the 10–15 h interval following induced spawning. Notably, significant differences (p < 0.001) were observed in these indices across different post-induction time intervals and between sexes. Throughout the breeding cycle, females demonstrated lower diversity and intensity in reproductive behaviors compared to males, suggesting distinct reproductive strategies between the sexes. The reproductive behavior of silver carp exhibited distinct chronobiological disorganization patterns. This study provides a scientific basis for future research on the behavioral ecology of silver carp and the conservation of their wild populations.

The middle reaches of the Yangtze River are a crucial breeding habitat for four major Chinese carps. The ecohydrological characteristics of their spawning grounds are crucial factors influencing spawning for these species: black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idella), silver carp (Hypophthalmichthys molitrix), and bighead carp (Aristichthys nobilis). To investigate the impact of ecohydrological processes within the Three Gorges Reservoir on spawning, this study focused on the spawning grounds of the four major Chinese carps in the Yichang–Yidu section of the Yangtze River. By identifying key ecohydrological indicators and leveraging hydrological and spawning monitoring data from 2013 to 2024, the response characteristics of the four major Chinese carps’ spawning to these hydrological processes were analyzed. The results showed that the key ecohydrological indicators currently stimulating spawning for the four major Chinese carps are the fish-perceived daily flow rate increase, the fish-perceived cumulative flow rate increase, and the daily flow rate increase. These three indicators are significantly positively correlated with the scale of spawning for the four major Chinese carps. The thresholds for spawning at least 20% of the annual spawning total are: a perceived daily flow increase (P_da) of 4.52–36.05%; a perceived cumulative flow increase (P_cu) of 36.15–180.23%; and a daily flow increase (Q_av) of 588–2825 m³/s. The optimal water temperature for the reproduction of the four major Chinese carps is 21–23 °C. Overall, since the Three Gorges Reservoir’s normal operation, the frequency and scale of spawning for the four major Chinese carps have been highest during periods of rising water. It is recommended that, within the corresponding thresholds, ecological operation be conducted twice a year, once in mid-June and once in early July or late June. Daily flow increases can be controlled within the range of 588–2000 m³/s. This study analyzed the correlation between eco-hydrological indicators and the stimulation of spawning of the four major Chinese carps, providing optimized flow ranges and habitat conditions for ecological operation, which is conducive to promoting the reproduction and spawning of the four major Chinese carps in the Yichang–Yidu spawning grounds in the middle reaches of the Yangtze River.

Cascade hydropower development in the upper Yangtze River has substantially altered riverine habitat conditions. However, quantitative information on fish substrate preferences remains limited. Based on field surveys, six representative substrate types were identified in the Yibin and Jiangjin reaches, and substrate selection patterns of Leptobotia elongata were quantified under controlled flume conditions. This study examined sex-specific and population-level differences in substrate preference. A total of 50 samples were analyzed using one-way ANOVA and the Kolmogorov–Smirnov test. The results are summarized as follows: (1) Substrates of 40–20 mm: Individual female L. elongata exhibited the longest residence time on the 40 mm substrate (1640 s), while individual males also spent the longest time on the 40 mm substrate (1549 s). Within this substrate range, males showed a preference only for the 40 mm substrate (PR = 739), whereas females preferred three substrate types, with the strongest preference for the 40 mm substrate (PR = 7543). (2) Substrates of 10–2.5 mm: Female individuals spent the longest time on the 10 mm substrate (1468 s), and male individuals likewise showed the longest residence time on the 10 mm substrate (1568 s). In this range, males did not show a significant preference for any substrate (PR = −907), whereas females preferred three substrate types, with the 2.5 mm substrate exhibiting the highest preference intensity (PR = 2059). (3) Population-level patterns for 40–20 mm substrates: The population spent the longest time on the 40 mm substrate (1799 s) and preferred three substrate types, among which the 20 mm substrate had the highest preference ratio relative to the other preferred substrates (PR = 4750). (4) Population-level patterns for 10–2.5 mm substrates: The longest residence time was observed on the 10 mm substrate (1762 s). The population preferred three substrate types, with the 10 mm substrate showing the highest preference ratio (PR = 5709). Overall, L. elongata showed a general tendency to prefer larger-sized substrates. This preference is likely associated with enhanced habitat complexity, improved foraging opportunities, and the formation of low-velocity refuges. Our results suggest that maintaining or restoring coarse substrate patches in regulated reaches may improve habitat suitability for L. elongata and potentially benefit other benthic fishes with similar ecological requirements.