3.2 Species compositions
Thirty-one species were collected, representing 11 families and 5 orders. Twenty-nine species occurred in both impoundments and free-flowing segments, of which the common species were Zacco platypus ,Acrossocheilus fasciatus , and Ctenogobius sp.(FO >40%), which were also abundance-dominant (RA >10%) except for A. fasciatus . The average species abundance per sample was 46.11 ± 29.43 (mean ± standard deviation [SD]) individuals in impoundments and 62.28 ± 39.49 (mean ± standard deviation [SD]) individuals in free-flowing segments, respectively. In addition, Ctenopharyngodon idella andMicropercops swinhonis (i.e., native-invasive species) were only collected in impoundments, whereas Leptobotia guilinensis andParasinilabeo assimilis (i.e., native species) only occurred in free-flowing segments (Table 1).
ANOSIM showed that fish assemblage composition strongly overlapped but significantly differed between the impoundments and free-flowing segments (Global R =0.04, P =0.014). The results of SIMPER analyses showed the differences in assemblage composition resulted from the abundance changes of 9 species between the two habitat types. Compared with the free-flowing segments, the abundances of four native (Z. platypus , Ctenogobius sp. , A. fasciatus , andVanmanenia stenosoma ) and one native-invasive (Rhodeus ocellatus ) species decreased in the impoundments, whereas that of three native-invasive (Misgurnus anguillicaudatus , Odontobutis potamophila , and Carassius auratus ) and one native (Cobitis rarus ) species increased (Table 2).