2.1. Sampling locations
Field surveys of fish were carried out from 2016 to 2018 at 50 sites on
rivers in three provinces (Hainan, Guangdong, and Guangxi) of South
China. Fish were systematically collected from eight main rivers:
Wanquanhe River (WQH), Nandujiang River (NDJ), Changhuajiang River
(CHJ), Jianjiang River (JJ), Moyangjiang River (MYJ), Dongjiang River
(DJ), Beijiang River (BJ), and Xijiang River (XJ) (Fig. 1). The lengths
of the sampled rivers are 160 km, 330 km, 232 km, 230 km, 199 km, 500
km, 445 km, and 2,100 km, respectively; the estimated catchment areas of
these rivers are 3,693 km2, 7,177
km2, 5,070 km2, 9,464
km2, 6,091 km2, 35,340
km2, 46,710 km2, and 353,120
km2, respectively (Pan, 1991). Each of the basins of
the eight rivers has a warm climate, abundantĀ rainfall, diverse native
fish species, and flourishing aquaculture operations (Huang, 2012).
However, the WQH, NDJ and CHJ are located in the tropics and have
relatively warmer temperatures (Huang, 2012). Furthermore, the study
rivers are considered to suffer severe invasions of non-native fish
species (Gu et al., 2018; Hu et al., 2020).