Risk Assessment Of Biological Invasion Of Important Alien Cultured Fishes

According to the"2020 China Ecological Environment Status Bulletin",more than660 invasive alien species have been found throughout China,of which 71 species are listed in the"China Invasive Alien Species List"as posing or potentially threatening to the natural ecosystem.The risk of invasive alien fish in China is increasing,characterized by rapid growth of invasive species,more diversified invasion channels and extensive involvement,which has caused serious harm to biodiversity,economic and social security.Although the introduction of alien fish has provided a great boost to the development of aquaculture and improved protein supply,the negative impacts of invasive alien fish on local species such as predation,intra-species competition,hybridization and disease transmission cannot be ignored.In recent years,various factors such as global climate change,basin-wide fishing bans,and aquaculture escapes have led to an increased risk of invasion of alien fish.In this study,we statistically analyzed the status of alien cultured fishes in China,and selected important alien cultured fishes with high culture production,wide range of culture areas,long culture history and high invasion risk.Based on the biological characteristics of the alien fish,the potential geographical distribution of an alien fish in China and its trends under the influence of various factors were predicted by the habitat suitability curve method.A data set of proximal environmental variables suitable for the analysis of aquatic organisms was screened,and the distribution of another alien fish in its suitability zone in China and its response to climate change were simulated by Max Ent,a maximum entropy model.The main findings were as follows.(1)Largemouth bass and Nile tilapia are important alien farmed fish in our country that urgently need to balance ecological risks and economic benefits.As of 2021,the three alien freshwater fish species with the highest annual production in China are:tilapia(about 1.663 million tons,with an average annual growth rate of 4.5%),largemouth bass(about 702,000 tons,with an average annual growth rate of 9.4%),and spotted forked catfish(about 363,000 tons,with an average annual growth rate of11.6%);among them,the annual production of tilapia has increased the most,and spotted forked catfish The annual output growth rate is the fastest.The alien aquaculture industry in China has grown significantly due to the increase in production,expansion of farming,market demand,and market acceptance of high-value alien aquaculture fish such as largemouth bass,tilapia,and spotted forked catfish.On the other hand,alien aquaculture fish have also invaded many of China’s wild waters,which may have a number of potential negative impacts,including declining biodiversity,degradation of habitat and ecosystem structure,disease transmission,and water quality degradation.Two important alien farmed fish species,largemouth bass and Nile tilapia,were selected as representative subjects to assess their potential distribution in natural waters based on various factors such as culture yield,culture range,economic benefits and invasion risks.(2)The prediction results indicate that largemouth bass has a broad habitat in China,and its invasion risk is exacerbated by multiple factors.The potential survival area of largemouth bass is spread throughout the country,and the potential spawning area is mostly in the southern basin.The potential spawning area of largemouth bass is mainly concentrated in the Pearl River basin,and the climate of the potential spawning area is dominated by subtropical monsoonal humid climate and subtropical humid climate.In the Yangtze River basin,the high-risk areas for largemouth bass invasion were mainly in the Jinsha River(tributaries of the Niulan River,the Pudu River and the Longchuan River)and the Gan River;the medium-risk areas were mainly in the Tuo River and the Xiang River;the low-risk areas were mainly in the Jialing River,the Han River and the Wu River;largemouth bass could spawn in the Niulan River and the Gan River in the Yangtze River basin,and almost the entire basin of the Yangtze River basin met the water temperature requirements for largemouth bass survival,regardless of habitat Without considering the effects of habitat fragmentation,largemouth bass may pose an invasive risk to the entire Yangtze River basin.The analysis showed that various factors,such as breeding escapes,climate change and reduced fishing pressure,led to the increased invasion risk of largemouth bass in the Yangtze River basin.(3)The prediction results indicate that Nile tilapia has a broad habitat in China,and its invasion risk is exacerbated by multiple factors.The Max Ent model simulated the potential distribution of Nile tilapia with good predictions,and the AUC values for all groups were higher than 0.88.The three key environmental variables affecting the distribution of Nile tilapia were:the average flow in the wettest month,the weekly minimum water temperature,and the number of weeks when the water temperature was less than or equal to 0.5℃.The current suitable areas for Nile tilapia are concentrated in the southern basins of the Pearl River,Yangtze River,southwest and southeast,and the total suitable area accounts for about 26.96%of the country,with the Pearl River basin(19.78×10~4km~2,37%)having the largest proportion of the highly suitable area.2081–2099 under the RCP8.5 climate scenario,the highly suitable area for Nile tilapia in China The size of highly suitability area for Nile tilapia in China increased to 77.20×10~4km~2in 2081–2099 under the RCP8.5 climate scenario,an increase of 42.64%(currently,54.13×10~4km~2).Under the influence of climate change,the middle and highly suitability areas of Nile tilapia have shifted southward,many low and middle suitability areas in the southern basin have been transformed into highly suitability areas,and the highly suitability areas also tend to expand to higher latitude basins.The comprehensive results show that largemouth bass and Nile tilapia are important alien cultured fish with wide range,high culture production,long culture history,high economic benefits and high invasion risks in China,and are in urgent need of balancing ecological risks and economic benefits.The potential spawning areas of Largemouth bass are concentrated in the southern basins such as Pearl River,Southwest,Southeast and Yangtze River basins in China,and water temperature is the most important environmental variable affecting its spawning,and there is a trend of expansion to high-latitude basins in the future under the influence of climate change.The suitable areas for Nile tilapia are distributed in the southern basins of Pearl River,Yangtze River,southwest and southeast basins in China,and there is a tendency to expand to higher latitude basins in the future under the influence of climate change.The most important environmental variables affecting the distribution of Nile tilapia are the mean flow of the wettest month,the minimum weekly water temperature,and the number of weeks with water temperature≤0.5℃.Predicting the potential distribution of important alien farmed fishes and their change patterns under the influence of various factors can help to curb the risk of biological invasion,protect the native habitat of native species,and provide useful references for the assessment,management,and prevention and control of alien fish invasion risk.