| The main rivers in south China are one of the most severely invaded areas by alien aquatic organisms in China,and there are 19 species of alien species distributed in the historical records.Clarias gariepinus and Lepisosteus spp.are the invasive alien fish in south China.C.gariepinus,commonly known as "Egypt moustache catfish",belongs to the Siluriformes,Clariidae,Clarias,native to Nile River in Africa,introduced into China in 1981 as a breeding and its characteristics of fast growth,high yield,individual large,omnivorous and characteristics of environmental tolerance.At present in our country are farmed in many areas.Lepisosteus spp.belongs to Lepisosteiformes,Lepisosteidae,native to north American freshwater lakes,introduced from the United States in 1990 as an ornamental fish,its snout protruding,with sharp teeth,crocodile-like,for the top carnivorous fish.Current research about C.gariepinus and L.oculatus has focused on geographical distribution and a small part on biological characteristics.However,the impact of these two exotic species on native fish stocks has not been assessed.Firstly,this study investigated the distribution of exotic fish in some river systems in Guangdong Province.Next,a comparative study on the functional response between the exotic fish C.gariepinus and native Silurus asotus was carried out through control experiments,and the population growth trend of the two species was simulated.Finally,a comparative study of functional responses between the exotic fish L.oculatus and native Channa maculate was carried out and simulated the population growth trend.The main conclusions are as follows:1.Preliminary investigation of exotic fish in multiple river systems in Guangdong Province.From August 2019 to October 2019,the survey was conducted at 10 sampling sites in xijiang River,beijiang River,dongjiang River(dongguan,heyuan),pearl river tributary and pearl river estuary.In sampling investigation to 10 kinds of alien fish,for example Cirrhinus mrigala ? Labeo rohita ? Prochilodus scrofa ? Colossoma brachypomum?C.gariepinus?Hypostomus plecostomus?Tilapia zillii?Oreochromis nilotica?O.mossambcus?including O.niloticus×O.mossambicus for new exotic fish,there is no record in the literature record;The total number of exotic fish accounted for 15.8% of the totally catched fish;The largest population is Cirrhinus mrigala?O.nilotica,?Tilapia zillii,accounting for 95.5 percent of the total alien fish.2.Comparison of the functional response and biological characteristics between exotic species C.gariepinus and native S.asotus.A comparative study was conducted on the functional responses of exotic species C.gariepinus and native S.asotus.Experiment with Cirrhinus molitorella,Megalobrama hoffmanni,Ctenopharyngodon idellus as feeding materials with bait density of 1,2,4,8,16,and 32,and three replicates were conducted.and three replicates were conducted.We analyzed the types of functional responses,constructed the curve of the functional response and fitted the parameters of the functional response.In addition,the food conversion efficiency and biological characteristics of C.gariepinus and S.asotus were compared.This experiment also analyzed the food conversion efficiency of C.gariepinus and S.asotus,and simulated the population growth trend of the two predators.The distribution of C.gariepinus in the whole country was reviewed by document system.The results showed that both C.gariepinus and S.asotus exhibit Type II functional response.Compared with S.asotus,C.gariepinus has a higher rate of unit resource consumption,that is,a stronger attack rate(P < 0.05),while the two species have no significant difference in prey handing time h(P = 0.272),the food conversion efficiency of C.gariepinus is significantly lower than(about 0.57 times)that of S.asotus(P < 0.05),There was no significant difference in the relative growth rate between these two species(P = 0.762).The population growth trend of C.gariepinus was significantly higher than S.asotus.It is learned from the article that C.gariepinus is farmed in 20 provinces,four municipalities and three autonomous regions in China,and has natural populations in all waters of south China,yibin and zigui sections of the upper reaches of the Yangtze river,anqing sections of the lower reaches of the Yangtze river,and xiaolan bottom and estuary sections of the Yellow River.3.A comparative study on functional responses of exotic species L.oculatus and native C.maculate.The experimental method is the same as experiment 2.The results showed that the survival rate of the three fry was 99.29 %.The functional response types of L.oculatus and native C.maculate were both Type II,and the two predators had similar functional response intensity.The relative growth rate of L.oculatus was higher than that of C.maculate(g,P < 0.05),while the differences in attack rate,processing time and food conversion efficiency between the two predators were not significant(a,P = 0.383;H,P = 0.663;E,P = 0.132);The increasing trend of the population biomass was slightly higher than that of C.maculate.4.According to the above studies,the functional response intensity of the exotic fish C.gariepinus is higher than that of the local S.asotus,and its population growth trend is higher than that of the S.asotus,so it may have a greater ecological impact.However,there was no significant difference in the rate of resource consumption between L.oculatus and C.maculate,and the population growth trend was slightly higher than that of C.maculate,indicating that it may not have a great ecological harm at present,but it looks like crocodiles and is prone to a strong social impact.Therefore,studies and prevention of these two exotic fish should be strengthened.In the future,on the basis of this study and in combination with the abundance and distribution area of these two exotic fishes,the ecological impact of these two exotic fish species can be more fully and quantitatively evaluated. |
PDF Full Text Request