Evaluation of the separation of triploid and diploid grass carp, Ctenopharyngodon idella (Valenciennes), by external morphology

The external morphology of diploid and triploid grass carp was studied to determine whether the two types could be separated by differences in external characteristics. In a comparison of 27 measurements, six scale counts and five fin formulae from two stocks of diploid and triploid fish obtained from commercial producers, analysis of covariance and discriminant analysis indicated a classification accuracy of only 65–85%. Clearly, triploid grass carp differentiated by external morphology alone should not be stocked into waters where diploid fish are illegal or would cause management problems.