3.2. Distribution variations
The weight ratio of non-native fish in the eight rivers averaged 26.6%, with a range of 4.7–45.5% (Table 1), and the amount ratio averaged 13.6%, ranging from 2.1% to 22.5% (Table 1). The number of non-native fish species in each river ranged from 8–14, with more non-native species found in the rivers of Hainan Island (i.e. NDJ, WQH and CHJ) as compared with the Continent rivers (i.e. JJ, MYJ, DJ, XJ and BJ) (F = 10.125, p = 0.019) (Table 1). The mrigal carp, rohu, and streaked prochilod were distributed only in the Continent rivers; the sutchi catfish, redhead cichlid, blackspot barb, mosquitofish, and walking catfish were distributed only in the Hainan Island rivers (Table 2).
According to the amount ratio of the different non-native species to the total number of fish collected (RN = NN1-X / NT), the rivers could be grouped into the Continent river assemblage and Hainan Island river assemblage; the Continent river assemblage could be further divided to into Continent coastal rivers (JJ and MYJ), the Pearl River system 1 (DJ and BJ), and the Pearl River system 2 (XJ) (Fig. 4). In the Hainan Island rivers, Nile tilapia, marble goby, and jaguar cichlid were the dominant fish species, with Nile tilapia recognized as an absolute dominant and the most common non-native fish species (Figs. 3, 4). In the Continent coastal rivers, Nile tilapia, redbelly tilapia, suckermouth catfish, and North African catfish could be recognized as dominant species, with Nile tilapia being an absolute dominant and the most common non-native fish species (Figs. 3, 4). In Pearl River system 1, the dominant non-native fish species in the two rivers were the same, comprising the redbelly tilapia, mrigal carp, and Nile tilapia; redbelly tilapia was an absolute dominant and the most common non-native fish species (Figs. 3, 4). In Pearl River system 2, none of the non-native fish species could be recognized as dominant species (Figs. 3, 4).
According to the amount ratio of different non-native species to the total non-native fish species catch (RN = NN1-X / NNT), the eight rivers could be divided to four assemblages: Hainan Island rivers, Continent coastal rivers (JJ and MYJ), Pearl River system 1 (DJ and BJ), and Pearl River system 2 (Fig. 5). In the Hainan Island rivers, the Nile tilapia, marble goby, jaguar cichlid, and redbelly tilapia were the most common non-native fish (Fig. 5). In the Continent coastal rivers (JJ and MYJ), Pearl River system 1 (DJ and BJ) and Pearl River system 2, the redbelly tilapia, Nile tilapia and mrigal carp were the most common non-native fish (Fig. 5).
Of the five most common non-native fish species, the amount ratio of marble goby, jaguar cichlid, and mrigal carp differed significantly between the Hainan Island rivers and Continent rivers, but the ratios of Nile tilapia and redbelly tilapia did not (Fig. 6). Temperature was significantly correlated with the amount ratio of Nile tilapia and redbelly tilapia, with that of Nile tilapia increasing along the mean minimum temperature of the coldest month (Fig. 7), and that of redbelly tilapia decreasing (Fig. 8).