Morphological variation analysis on escaped Nile tilapia from main aquaculture areas in Guangxi

ObjectiveThis research was conducted to elucidate the effects of geographical habitat on morphological variation of escaped Nile tilapia to provide reference for future study of tilapia population invasion and formulation of con-trol strategy.MethodThe one-year-old male escaped N. tilapias from six main aquaculture areas(Yulin,Nanning,Qin-zhou,Guigang,Fangchenggang and Beihai)in Guangxi were collected. Morphological characteristics and multivariate morphometrics were analyzed by morphometry,principal component analysis,discriminant analysis and cluster analysis.ResultIn terms of full length,body length,body height,head length,snout length and body weight,N. tilapias from Yulin were the largest while those from Qinzhou the smallest,and significant difference was observed between tilapias from the two areas(P<0.05). In principal component analysis,the contribution rates of top three principal components were 74.31%,9.23%and 6.21%,cumulative contribution rate reached 89.75%,which summarized growth characteristics of wild escaped N. tilapias in different aquaculture areas. Discriminant analysis showed that N. tilapias from different aquaculture areas could be distinguished by using discriminant function established based on seven morphological charac-teristics including full length,body thickness,head length,snout length,eye diameter,eye distance and body weight, and the discriminant accuracy was 96.11%. Cluster analysis suggested that the N. tilapias in Qinzhou had the lowest simi-larity with those from other regions but the largest variation,and thus appeared as a single clade. The correlations between body weight and full length,body length,body height,body thickness,head length,snout length,eye diameter and eye distance were extremely significant(P<0.01). Thereinto,correlation coefficients between body weight and full length, body length and body height were high,reaching 0.9375,0.9359 and 0.8327 respectively,but its correlation coefficient with eye diameter was the lowest(0.5947).ConclusionPrincipal component analysis and discriminant analysis are feasi-ble methods to distinguish the source of escaped tilapia. Analysis on full length,body length and body weight of escaped N. tilapia can be helpful for understanding its living condition and provide reference for controlling tilapia invasion.