Analysis of fish community structure and elological niche in upstream and downstream of Changzhou Dam in Guangxi

【Objective】 The aim of the study was to comprehensively analyze the upstream and downstream fish community structure and major fish temporal-space ecological niche of Guangxi Changzhou Dam，and provide reference basis for the rational operation of fish passage and its upstream and downstream fish resources and habitat protection of Changzhou Dam in Guangxi. 【Method】 The fish resources status in upstream and downstream of the Changzhou Dam was investigated in 4 consecutive seasons in July-August 2022（summer），November 2022（autumn），February 2023（winter）， and May 2023（spring），and the dominant species were identified by using the Pinkas relative importance index（IRI）， and the spatial differences in fish community structure was analyzed by applying the non-metric multi-dimensional disordering（NMDS），the correlation between major fish species and environmental factors was explored by redundancy analysis of selection（RDA），and the spatial and temporal ecological niches of major fish species were assessed by ecological niche breadth（B_ij）and ecological niche overlap index（Q_ik）. 【Result】 A total of 2669 fish samples were collected，belonging to 13 orders，26 families，66 genera and 80 and dominated by sedentary，omnivorous and demersal fishes，with migratory fish greatly reduced. The dominant species in the upstream and downstream fish communities of the Changzhou Dam included Megalobrama terminalis，Squaliobarbus curriculus，Parabramis pekinensis，Cirrhinus molitorella and Culter recurviceps，and the seasonal changes of the downstream fish communities were more obvious than that of the upstream fish communities. Water pH，temperature and dissolved oxygen were the main environmental factors affecting the structural and distributional characteristics of the upstream and downstream fish communities in the Changzhou Dam. The spatial ecological niche breadth of the main fish species in upstream and downstream of the Changzhou Dam varied from 0.640 to 0.693，and the temporal and spatial niche breadth ranged from 0.436 to 0.960，belonging to the narrow niche species，that was，the utilization of resources by fish was poor，and the adaptability to the environment and spatial competitiveness were weak. The spatial niche overlap index ranged from 0.904 to 1.000，all of which were significantly overlapped（Q_ik>0.6），that was，the utilization of resources by fish was extremely similar. 【Conclusion】 There is no great difference in the fish community structure between the upstream and downstream of Changzhou Dam，indicating that the fishway provides a guarantee for the exchange of fish communities between the upstream and downstream. However，a few fish species，such as M. terminalis，Hilsa reevsii，Cynoglossus trilineatus and Clupanodon thrissa，are still affected. Therefore，the Changzhou Dam fishway should be comprehensively considered in terms of operating water level and operating time. At the same time，it is necessary to increase the intensity of proliferation and release，standardize the fishing methods of fishermen，and continue to implement the fish ban system.