Analysis On The Status And Morphological Differences Of Tialapia Stocks In Main Rivers Of Southern Guangxi

Since the introduction of tilapia as a good breeding species in China in 1956,the scale of tilapia farming has been expanding.Today,tilapia farming industry is widely distributed in South China.China has become the largest tilapia farming,processing and trading country in the world.However,due to poor management and other human factors,a large number of tilapia escaped and spread to natural waters,resulting in serious biological invasion and many serious consequences,such as the destruction of local original habitats,breaking the ecological balance,the decline of biodiversity,and the sharp decline or even extinction of many indigenous fish stocks.At present,there are few reports on Tilapia invasion in Guangxi.It is imperative to carry out systematic research This study investigates and analyses the invasion of tilapia in Xunjiang,Yujiang,Qianjiang,Zuojiang,Youjiang and Yongjiang rivers,which are the main rivers in southern Guangxi.The purpose is to understand the specific situation of the invasion of tilapia into rivers and to put forward corresponding countermeasures to alleviate the ecological and economic problems caused by the invasion of tilapia.Through the research,the following results are obtained:(1)Wild tilapia populations were found in the main waters of southern Guangxi,Mainly is Oreochromis niloticus,Coptodon zillii and Oreochromis mossambicus a total of 1354 tilapia samples were collected,of which 739 were nile tilapia,579 were redbelly tilapia and 36 were mozambique tilapia.The age of wild tilapia population was determined,and it was found that there were more than 2-year-old individuals in all the sites,which indicated that wild tilapia population could overwinter under natural conditions.The gonad analysis showed that the gonad development of wild tilapia was good.The individuals whose ovaries developed to stage IV and above accounted for 55.86%of the total female samples,indicating that reproductive activities could be completed in the field.The correlation analysis between body length and body weight and the analysis of fatness showed that wild tilapia grew well in the field.The individual absolute fecundity of Longzhou redbelly tilapia population was the largest,averaging 5363 grains,while that of Pingguo redbelly tilapia population was the smallest,averaging 1669 grains.The longest relative fecundity of Pingguo redbelly tilapia population was 43 grains/mm,the largest relative fecundity of body mass was 63 grains/g,and the smallest relative fecundity of body length and body weight appeared in Longzhou,11 grains/mm and 13 grains/g,respectively.The individual absolute fecundity of Baise nile tilapia population was the largest,with 4531 grains,and the smallest was in Tianyang,with 832 grains.The maximum relative fecundity of body length and body weight appeared in Chongzuo,21 grains/mm and 19 grains/g respectively;the minimum relative fecundity of body length was 5 grains/mm,which appeared in Nanning and Tianyang sampling sites;and the minimum relative fecundity of body weight was 3 grains/g,which appeared in Guigang sampling site.(3)Through principal component analysis,it was found that the morphological differences of tilapia populations at different sampling points were mainly reflected in head,tail and trunk characteristics.The results of principal component analysis showed that the morphological characteristics of the nile tilapia population had certain similarities,and showed a high similarity with the tilapia population at the sampling points of the water system.Stepwise discriminant analysis was used to discriminate different tilapia populations.The results showed that the comprehensive discriminant rate of tilapia population was low,only 48.2%.The low discriminant rate indicates that the morphological differentiation of wild tilapia population is not obvious,and there may be interaction among the populations at different sampling points.Cluster analysis showed that the morphological distances between Pingguo Nile tilapia population and other sampling sites were large,while the morphological performance of other sampling sites was almost the same.Therefore,it is believed that the morphological characteristics of wild tilapia populations have not changed much,that is,the morphological differences are very small.Through principal component analysis,the morphological differences of redbelly tilapia population can be reflected by the characteristics of kiss,trunk(left and right axes and dorsal-ventral axes)and tail.The results showed that the morphological characteristics of all the redbelly tilapia populations had certain similarities,and showed high similarities with the tilapia populations of the water system sampling points.The results of stepwise discriminant analysis showed that the comprehensive discriminant rate of redbelly tilapia population was 62.8%.The morphological differentiation of red-bellied tilapia population was not obvious and could not be accurately discriminated.At the same time,there might be interaction among different sampling points.Cluster analysis showed that the mor:phological distance between Pingguo red-bellied tilapia population and other sampling sites was larger,while the morphological performance of other sampling sites was almost the same.Through this study,it is proved that the tilapia population has been successfully established in the rivers of southern Guangxi,and can successfully complete overwintering and reproductive activities.The fecundity study found that the fecundity of invasive tilapia was lower than that of domestic and foreign research results.Through morphological analysis,It was found that there was no significant difference in morphological structure of invasive tilapia(except Pingguo population)in the main rivers of southern Guangxi.