Diet partitioning and trophic guild structure of fish assemblages in Chishui River, the last undammed tributary of the upper Yangtze River, China

Knowledge of trophic ecology of fish species is fundamental to understand the organization mechanism of fish assemblages and crucial for developing effective management and conservation strategies. This study examined the diet partitioning and trophic guild structure of fish assemblages in Chishui River, the last undammed tributary of the upper Yangtze River, China. Specimens were collected in three sections along the upstream-downstream gradient in 2012. Digestive tract contents of 54 fish species, represented by 692 individuals, were analysed and quantified. Analysis showed that fish assemblages in the Chishui River utilized aquatic insects, algae, detritus, molluscs, and fishes as the main food resources, whereas terrestrial insects were consumed only occasionally. The trophic guild structure of fish assemblages changed gradually with the longitudinal gradient. Specially, the number of trophic guilds increased with downstream distance. In addition, the relative number of omnivorous species increased longitudinally, whereas the relative number of insectivorous species declined downstream. This study demonstrated how fish assemblages utilize the food resources under near-natural conditions. These results provide valuable information for fish conservation and ecological restoration.