Abstract: Heishui River, located in the lower reaches of the Jinsha River, is an important habitat and a priority tributary for fish conservation in the mainstream of the Baihetan Reservoir area. The structure of fish communities in Heishui River has been changed due to human activities, such as hydropower station construction, overfishing, and sand excavation from river channels. The aim of this study was to understand the status of fish resources and to provide a scientific basis for fish resources protection and ecological restoration in Heishui River. Quarterly samples were collected at 23 sampling sites in Heishui River from November 2018 to September 2019. Fish samples were collected by gill nets (outer mesh 7 cm, inner mesh 2-3 cm, net height 2 m, net length 80 m) and cages (12 m×0.4 m×0.4 m). Species identity, body weight and body length of all fish collected at each sampling site were determined. During the surveys, a total of 44 fish species were identified belonging to 4 orders, 10 families, and 33 genera, with 11 species being endemic species of the upper Yangtze River. Paracobitis varigatus, Schizothorax wangchiachii, Triplophysa daqiaoensis, Zacco platypus, Paracobitis potanini and Glyptothorax sinense were the dominant fish species in Heishui River, which accounted for 28.44%, 28.01%, 16.66%, 7.18%, 5.09% and 3.36% of the total weight of captures, respectively. The similarity of fish community composition between the upper reaches of Sujiawan Dam and the lower reaches of backwater point 765 in Heishui River was the lowest (24.32%), whereas the upper reaches of the Sujiawan dam and the reaches from Songxin dam site to Laomuhe dam site was the highest (61.90%). The results of autecology matrix analysis showed that the fish community in Heishui River was mainly composed of riffle, with lower mouth, and omnivore group. The fish diversity index showed an increasing tendency from upstream to downstream of Heishui River, with no variation of diversity index among different seasons (P>0.05). Abundance biomass comparison (ABC) curve showed that the structure of the fish community in Heishui River was moderately disturbed. Our results suggested that the fish in Heishui River exhibited a trend of miniaturization compared with historical data, and consequently the protection measures should be strengthened.

Key words: fish resource, Heishui River, diversity index, abundance biomass comparison curve.