Feeding ecology of Acrossocheilus yunnanensis (Regan, 1904), a dominant fish in the headwaters of the Chishui River, a tributary of the Yangtze River

Feeding ecology of Acrossocheilus yunnanensis, a dominant fish in the headwaters of the Chishui River, a tributary of the upper Yangtze River, was studied using the analysis of gut contents. From March 2015 to January 2016, a total of 543 individuals were collected and analyzed. The results showed that A. yunnanensis was an omnivorous fish mainly feeding on chlorophytes, diatoms, and aquatic insects. The trophic level was 2.69 +/- 0.62 (mean +/- SD), signifying A. yunnanensis as a primary or secondary predator. Dietary shifts were found among different ontogenetic stages and seasons. Specifically, young individuals fed primarily on aquatic insects and diatoms, whereas older fish fed mainly on chlorophytes. In spring, the preferred food item was aquatic insects and in other seasons, chlorophytes became the predominant prey. Diet composition showed no differences among individuals of different sex and diel periods. The feeding intensity of A. yunnanensis was not affected by diel periods, suggesting this species feeds continuously. However, its feeding intensity was significantly influenced by seasons. Pairwise comparison found that the feeding intensity was higher in spring and autumn than that in summer and winter, with minimum food intake in winter and maximum in spring. Analysis on Amundsen graph and niche breadth index indicated that A. yunnanensis might pursue an opportunistic and moderately generalized feeding strategy, which could explain why it has become the dominant fish species in our study area