Status and ecological risk assessment of alien fish in the Yangtze River basin

In order to ascertain the current status and ecological risks of alien fishes in the Yangtze River basin, we compiled a list of alien fish species in the Yangtze River basin based on various sources, and the Aquatic Species Invasiveness Screening Kit (AS–ISK)was used to evaluate the risk of alien fishes.The results showed that: (1) There are 38 species (belong to 29 genus, 15 families, 8 orders) of alien fishes in the natural waters of the Yangtze River basin, including cypriniformes (17 species), Siluriformes(7 species), Perciformes(5 species), Acipenseriformes(4 species), Characiformes(1 species), Cyprinodontiformes(1 species), Osmeriformes(1 species), Lepisosteiformes(1 species), the largest number of alien fish from Asia (17 species), and most of the introduction purposes are aquaculture (20 species). (2) Alien fishes have been widely distributed in various rivers and lakes in the Yangtze River basin, and the mainstream of the Three Gorges Reservoir has the largest number of species (22 species). (3) Based on the basic risk assessment of the AS–ISK, 19 species of fish were classified as high risk, 6 species as medium risk, and 13 species as low risk. The five species with the highest risk scores are Gambusia affinis, Hypostomus plecostomus, Oreochromis niloticus, Micropterus salmoides and Oreochromis mossambicus. The results show that the alien fishes in the Yangtze River basin present a large number of species and complex distribution pattern. Currently, no serious negative impact of alien fishes on the ecological security of the Yangtze River basin has been found, but the risk level assessment results indicate that alien fishes have extremely high potential hazards. The results of this study can provide important data and theoretical reference for the prevention and control and management of alien fish in China.