Species composition of fish in the Chishui River
In this study, we conducted a comparative analysis of 77 fish species, accounting for 54% of the species studied (Liu et al., 2021). Of the 77 species, 72 were known fish species, including seven medium exotic fish species and five new fish species. Our findings revealed that Cypriniformes, Siluriformes, and Perciformes were the dominant orders (Figure 1b), which is consistent with the results of previous studies (Liu et al., 2021). Additionally, our results indicated that Cyprinidae, Balitoridae, and Bagridae were the dominant families in the Chishui River, which is consistent with earlier studies (Liu et al., 2020; Liu et al., 2021).
The five new fish species in the Chishui River include: Acipenser sinensis , Schizothorax prenanti , Euchiloglanis davidi ,Rhynchocypris lagowskii , and Cirrhinus molitorella .A. sinensis is a migratory fish (Boscari et al., 2022) that was once commonly found in the Yangtze River Basin. In the present study, we detected 142 OTUs of A. sinensis near a river estuary. Although Chinese sturgeons are known to be released and bred in the upper reaches of the Yangtze River, the presence of A. sinensis in the Chishui River is likely due to human influence rather than a wild population (Yang et al., 2023).
S. prenanti , another new fish species found in the Chishui River, is typically distributed in the upper reaches of the Yangtze, Guizhou, and Sichuan Rivers. We believe that its presence in the Chishui River is due to its occurrence in the surrounding areas. E. davidi ,R. lagowskii , and C. molitorella were also identified. These fish species were confirmed through interviews with local fish experts as individual catches were reported in the area.
Notably, the eDNA technology used in this study to detect fish species can only identify species sequences. Thus, although the presence of these fish species in the Chishui River was confirmed, further research is needed to determine their abundance, distribution, and potential impacts on the ecosystem.
Seven alien species were identified: Ictalurus punctatus ,Clarias gariepinus , Gambusia affinis , Rhynchocypris oxycephalus , Barbatula nuda , Cirrhinus molitorella , andMicropterus salmoides . Of these species, R. oxycephalusand B. nuda have demonstrated strong adaptability to the Chishui River environment, establishing wild populations and occupying certain ecological niches. However, this could threaten the ecological balance of the river (Tang et al., 2021).
I. punctatus is a fast-growing carnivorous fish with a broad range of food habits that primarily feeds on aquatic insects and small fish. Under certain conditions, it may pose a greater threat to rare juveniles or other fish species. Similarly, M. salmoides andC. gariepinus , both carnivorous fish with strong environmental adaptability, have the potential to prey on the juveniles of local fish species and force indigenous species to switch habitats through interspecific competition (Zhang et al., 2022; Zhao et al., 2020). This ultimately affects the distribution of these species (Li et al., 2016).
The omnivorous G. affinis has been reported to consume a large number of eggs and juveniles of local fish species in invaded areas, leading to a significant decline in their populations (Goodsell and Kats, 1999).