Fish community diversity and environmental influencing factors in Poyang Lake before the fishing ban

As an important component of aquatic biodiversity, fish are the most sensitive and reliable indicator of ecosystem function in aquatic areas. Its growth and development are closely related to the environmental factors of the inhabiting waters, and have an important indicator of environmental changes. In order to grasp the characteristics of the fish community in Poyang Lake, we conducted fish resource surveys in ten regions of Poyang Lake involving five habitats and collected water environment samples simultaneously in spring (May), summer (August), autumn (November) of 2020 and winter (January) of 2021 before the comprehensive fishing ban. We identified a total of 67 fish species, belonging to 8 orders 14 families 47 genera, of which Cyprinidae had the the maximum no. of species, accounting for 61.19%. According to different groups, the dominant ecological types of fish were mainly lake sedentary (61.19%), omnivore (44.78%), and lower fish (35.82%). Small fish was the dominant group in this community, accounting for 68.70%, and the index of relative importance (IRI) showed that there were six dominant species, the first one was Pseudobrama simoni. Significant seasonal differences were observed in fish community structure (P<0.05), and the fish species diversity index in spring was higher than that in winter (P<0.05), because the diversity and richness of species were affected by seasonal factors. Changes in water temperature and water level may be the main reasons for affecting the spatial and temporal pattern of fish community diversity in Poyang Lake. Non-metric multidimensional scaling analysis (NMDS) showed that fish could be spatially divided into two taxa, namely the estuary taxon and the grassy-lake branch-lake center-coastal zone taxon. In redundancy analysis (RDA), we observed that total phosphorus, chlorophyll a and transparency were key environmental factors affecting the spatial and temporal distribution of fish species. With the change of hydrological rhythm in the lake area, with the increase of water level, nutrients flow into the lake area, providing a rich food source for fish, and fish feeding activities are enhanced. When the total phosphorus is too high, it will lead to eutrophication of the water body, and the nutrient load and suspended solids will limit the habitat and even survival of sensitive species. Chlorophyll a is an important indicator reflecting the change of phytoplankton content, and in spring, with the increase of temperature, the surface water temperature rises rapidly, and phytoplankton in the water body begins to multiply in large quantities, which is reflected in the increase of surface chlorophyll a content. Abundance-biomass comparison curve (ABC curve) analysis showed that the fish community was severely disturbed (W=−0.091). This study can provide a scientific basis for the evaluation of the effect of fishing ban and the conservation of fish diversity in Poyang Lake.