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).