3.1. Species composition
The total catch from the eight rivers comprised 98,887 individual fish,
of total weight 6,525.65 kg. The total catch per river survey averaged
815.70 kg (range 542.62–1,388.86 kg), and the average number of fish
caught per river was 12,361 (range 6,579–28,293) (Table 1). The number
of fish species caught in each river averaged 84 and ranged from 55 to
136.
A total of 11,832 individual non-native fish, of total weight 1,531.90
kg, were caught in the eight rivers. Twenty non-native fish species were
found: Nile tilapia, redbelly tilapia, suckermouth catfish, mrigal carp,
North African catfish, marble goby Oxyeleotris marmorata(Bleeker), rohu Labeo rohita (Hamilton), streaked prochilodProchilodus lineatus (Valenciennes), jaguar cichlid, Mozambique
tilapia Oreochromis mossambicus (Peters), blue tilapiaOreochromis aureus (Steindachner), red pacu Piaractus
brachypomus (Cuvier), sutchi catfish Pangasianodon hypophthalmus(Sauvage), redhead cichlid theraps maculicauda Cichlasoma
synspilum (Regan), blackspot barb Dawkinsia filamentosa(Valenciennes), channel catfish Ictalurus punctatus (Rafinesque),
redbreast tilapia Coptodon rendalli (Boulenger), galilaea tilapiaSarotherodon galilaeus (Linnaeus), mosquitofish Gambusia
affinis (Baird & Girard), and walking catfish Clarias batrachus(Linnaeus).
The 20 non-native fish species collected represent 5 orders, 10
families, and 16 genera (Table 2); the orders most represented were the
Perciformes, Siluriformes and Cypriniformes, with 9, 5 and 4 species,
respectively (Fig. 2a). Of the non-native species, 16 are used for
aquaculture, 3 in the ornamental fish trade, and 1 for biocontrol (Fig.
2b). Seven of the non-native species originate from Africa, 5 from
Southeast Asia, 4 from South America, 2 from Central America, and 1 each
from South Asia and North America (Fig. 2c). Of the 20 non-native
species, 13 are omnivores and 7 are predators (Fig. 2d).
The non-native fishes collected in the greatest proportions were Nile
tilapia (46.31%, n = 5,479), redbelly tilapia (28.52%, n= 3,375), jaguar cichlid (7.38%, n = 873), marble goby (6.61%,n = 782), and mrigal carp (4.09%, n = 484). Based on the
values of IRI, Nile tilapia was the dominant fish species in seven of
the rivers (not in XJ), and could be recognized as an absolute dominant
fish species in five of the rivers (NDJ, WQH, CHJ, JJ and MYJ) (Fig. 3).
The redbelly tilapia was the dominant fish species in four of the rivers
(BJ, DJ, JJ and MYJ), and could be recognized as an absolute dominant
fish species in two of the rivers (BJ and DJ) (Fig. 3). Mrigal carp was
the dominant fish species in three of the rivers (BJ, DJ and MYJ);
marble goby was the dominant fish species in CHJ and WQH; and jaguar
cichlid was the dominant fish species in NDJ and WQH (Fig. 3).