Fish diversity responds to environmental variables and anthropogenic activities
In this study, we found that changes in distribution and diversity in the Chishui River Basin were predominantly influenced by environmental factors. The results of our CCA showed that altitude had a significant impact on upstream fish richness, resulting in a significant decrease in fish species richness with increasing altitude. Similarly, conductivity significantly affected downstream fish richness (Chen et al., 2020). Our findings demonstrated a significant decrease in fish species richness with increasing conductivity. Previous studies have highlighted the importance of these two factors in affecting fish species richness. The altitude difference between the upper and lower reaches of the Chishui River can reach 1180 m, leading to changes in water temperature and flow rate. These changes resulted in noticeable differences in upstream, middle, and downstream fish habitats, leading to variations in fish species composition. For instance, Sinocrosssocheilus labiatusand other fish adapted to cold-water environments were only found in the upstream basin in this study, leading to specific fish species upstream that exhibited significant differences from those downstream.
Human activity in the downstream basin is more intensive than in the upstream reaches, resulting in increased water pollution and impurities. As a result, most fish are intolerant of this environment (Bertora et al., 2022), leading to a decrease in fish species. However, tolerant fish species, such as Zacco platypus , have shown an increase in population numbers (Yeom et al. 2007; Morosawa 2011). In summary, our research showed that environmental factors such as altitude and conductivity play a significant role in the distribution and diversity of fish species in the Chishui River Basin.
This study found that the impact of anthropogenic activities, specifically the use of fertilizers, pesticides, and land, on the study area was not significant. Based on our analysis, we believe that this result can only be considered valid under the assumption that the intensity of anthropogenic activity in the Chishui River Basin has not yet reached the threshold affecting fish diversity. Additionally, human influencing factors, such as fishing intensity, disappeared after the implementation of the fishing ban. This policy has led to fish in the Chishui River Basin being primarily affected by environmental factors, which is similar to the natural succession stage and conducive to the community reconstruction process (Liu et al. 2021). In summary, the results of this study suggest that the current environmental conditions in the Chishui River Basin are favorable for community reconstruction.