4.1. Distributions of the non-native fishes and their potential impacts
Non-native fish species appear to be common and widespread in the freshwaters of South China, as they were recorded in all eight main rivers (Table 2). Although not all of the 20 species can be classified as invaders, all the rivers have been colonized by multiple non-native fish species.
Of the 20 non-native fish species found, the Nile tilapia, redbelly tilapia, mrigal carp, North African catfish, and suckermouth catfish are considered the most successful invaders because: (1) they were found in all of the studied rivers (Table 2); (2) they have established self-sustaining populations and can be considered as dominant fish (Fig. 3); and (3) they have negatively impacted native fish species and water quality (Gu, Hu et al., 2018; Yu et al., 2018). The marble goby and jaguar cichlid appeared to be successful invaders in the NDJ, WQH and CHJ of Hainan Island, where they have established natural populations and impact native species through predation (Figs. 3, 7) (Wang et al., 2012; Yu et al., 2018). These invasive fishes can cause a series of impacts on the region’s biodiversity and economy. For example, the invasion of tilapia in Guangdong Province has caused economic losses in the cultured and capture fisheries, leading to species exaction, biodiversity loss, and deterioration of the natural aquatic environment (Gu, Yu, et al., 2019).