4.2. Factors influencing the non-native fish species composition
Vectors of fish translocation and introductions include the aquarium
trade, aquaculture rearing, fisheries stocks, and biological control
(Li, Dong, Li & Wang, 2007; Glozan, 2008; Xiong, Sui, Liang & Chen,
2015; Gu, Hu, Xu, Wei, Luo, et al., 2018). Of the 20 non-native fish
species found in South China, 16 are aquaculture species, and 6 of the 7
invasive fish species were introduced for aquaculture rearing (Fig. 2b).
Fish inadvertently introduced from aquaculture facilities typically have
a strong ability to tolerate a range of environmental conditions,
flexible habitat requirements, efficient reproductive strategies, and
fast growth, as compared with fish species cultured for the ornamental
trade (Canonico, Arthington, McCrary & Thieme, 2005; Martin, Valentine
& Valentine, 2010). For example, Nile tilapia is one of the most
popular cultured fishes
and
it has become perhaps the most widely distributed invasive species
globally (Zambrano, Martinez, Menezes, & Peterson, 2006; Gu, Yu, et
al., 2019). Therefore, vigilant management is needed to prevent the
escape of cultured non-native fish species from aquaculture facilities.
All of the non-native fish species found in the eight rivers are native
to tropical freshwaters, except for the channel catfish, which is native
to North America, and all of the successful invasive fish species in
these rivers of South China are native to the tropics (Li, Dong, Li &
Wang, 2007; Hu, Dong, Hao & Gu, 2020) (Fig. 2c). The rivers surveyed in
this study have the warmest climates in China and their environmental
conditions are similar to the native habitats of the non-native fish
species (Huang, 2012). Furthermore, among the eight rivers, more
non-native fish species were found on Hainan Island (NDJ, WQH, CHJ),
where the rivers are tropical and warmer (Table 1). Although the region
of the study contains most of the non-native fish species cultured in
China, many species native to colder areas, such as largemouth bassMicropterus salmoides , were not found in the rivers. This result
suggests that, in this region, alien fish species originating from
regions with similar geographical conditions will best survive and
spread easily.
Thirteen of the non-native fish species found are omnivores, and 7 are
predators (Fig. 2d). Of the 7 successfully invasive species, the North
African catfish, marble goby, and jaguar cichlid are effective
predators, whereas the Nile tilapia, redbelly tilapia, mrigal carp, and
suckermouth catfish are typical omnivores. Fish predators may succeed in
a new environment when their prey are not adjusted to their particular
style of predation (Moyle & Light, 1996). Omnivores that forage on
low-quality resources may succeed because such food resources are rarely
limiting in aquatic systems (Moyle & Light, 1996; Gido & Franssen,
2007; Gu, Mu, et al., 2012; Gu, Hu, Xu, Wei, Luo, 2018). Accordingly, a
species’ trophic position may be a key factor in its colonization and
invasion capacity, and top predators and omnivores are most likely to be
successful invaders in the rivers of South China.