STUDY ON MORPHOLOGICAL VARIATION AND DISCRIMINATION OF WHITE SHRIMP (EXOPALAEMON MODESTUS HELLER) AMONG POPULATIONS OF FIVE LARGE LAKES IN CHINA

White shrimps(Exopalaemon modestus Heller)were collected from Taihu Lake,Poyang Lake,Chaohu Lake,Hongze Lake and Dongting Lake in China.Eight morphological traits of 326 shrimps were measured and ten morphological proportional parameters were formed after adjusting.Morphological variation among populations was calculated using three kinds of multivariate analysis techniques.The variance contribution ratios of the first three principal component were 31.216%,21.577% and 15.239%,respectively,and the cumulate variance contribution ratio was 68.032%.The results of principal component analysis showed that morphological variation among five populations lied mostly on three ratios of ventral width to body length,ventral width to ventral length and head-cuirass width to body length.Cluster analysis showed that the populations from Taihu Lake and Poyang Lake formed a common cluster firstly,then Chaohu Lake,Hongze Lake and Dongting Lake joined to the cluster in turn,which revealed the least variations between Taihu Lake and Poyang Lake and the most variations between Taihu Lake and Dongting Lake.Discriminant functions were established for five populations.The discriminant accuracy was from 66.7% to 96.7% and the synthetic identification discriminant analysis accuracy was 80.7%.Coefficients of difference were calculated.According to Mayr's 75% rule,the differences among different populations of Exopalaemon modestus are stil1 within the population level and do not reach the subspecies level.Morphological differences between different populations appear to result from both genetic differences and environmental factors.