3.1 Species composition
A total of 1330 individuals, represented by 21 fish species, were collected during the sampling period (Table 2). These species were belonged to 3 orders, 8 families and 19 genera. Of these,Leptobotia hansuiensis were endemic to upper Han River drainage,Scaphesthes macrolepis and Schizothorax prenanti have been assessed as vulnerable by the China Species Red List (Jiang et al., 2016). Cypriniformes was the most abundant order, represented by 17 species and accounted for 91.0% of the total species, followed by Perciformes (3 species) and Siluriformes (1 species). Cyprinidae was the major dominated family, represented by 13 species and accounted for 61.9 % of the total species. The remaining families comprised only one to three species.
The most common and abundant species was Rhynchocypris oxycephalus , which occurred in 71.7% of the sampling occasions and accounted for 50.3 % of the total number of specimens captured. The next most abundant species was Gnathopogon herzensteini , which accounted of 9.6% the total number of specimens, followed byMetahomaloptera omeiensis (9.4 %), S. macrolepis (8.5 %), and Zacco platypus (5.3 %). Some species, such asHemibarbus maculates , Pseudogobio vaillanti ,Spinibarbus sinensis and S. prenanti , just occurred occasionally.