Risk assessment of invasive fish species in the middle and upper reaches of the Yangtze River (including Dongting Lake)

To understand the current status of exotic fish in the middle and upper reaches of the Yangtze River and to assess their invasion risks, investigations on exotic fish were conducted using fixed gill nets, drift nets, and ground traps at 22 river sections of the main stream and tributaries of the middle and upper reaches of the Yangtze River, as well as at Dongting Lake and Honghu Lake from May to July and from October to December in 2022. The results showed that a total of 135 species of fish belonging to 8 orders, 24 families, and 20 species of exotic fish were collected during the survey period. The investigation in the Jiangjin section revealed the highest number of exotic fish species, with the highest occurrence frequency being the exotic sturgeon. Through the Fish Invasion Screening Test (FIST), six high risk invasive fish species were preliminarily screened, including Oreochromis niloticus, Coptodon zillii and Cyprinus carpio. Further analysis of invasion risk was conducted using the Fish Invasion Screening Kit (FISK), and a total of 8 species of fish were identified as high invasion risk, C. zillii, Clarias lazera and Cirrhina mrigalancluding. The ROC curve was used to validate the FISK scoring results, which showed an AUC value of 0.944, indicating that the FISK evaluation method has a high ability to distinguish species invasiveness and can distinguish whether foreign fish have invasion risks in the study water under current and climate change scenarios. Research has shown that based on the risk assessment results of invasive fish species mentioned above, there are already multiple high-risk fish species in the middle and upper reaches of the Yangtze River, which may seriously endanger the fishery resources and the structure and function of the aquatic ecosystem in the middle and upper reaches of the Yangtze River. It is recommended to increase the management and control of high-risk invasive species, while strengthening the protection of indigenous fish populations, in order to avoid significant damage to the Yangtze River indigenous fish resources caused by invasive species. This study can provide countermeasures for the protection of Yangtze River indigenous fish resources.