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Twenty-six morphological and meristic characters of diploid and triploid hybrids between female grass carp, Ctenopharyngodon idella and bighead carp Hypophthalmichthys nobilis were analyzed by discriminant-function analysis. Twelve characters were useful in distinguishing between diploids and triploids. When these 12 characters were subjected to discriminant-function analysis, 97% of the hybrids were correctly classified as either diploid or triploid. No single character allowed diploids to be distinguished from triploids. Triploid hybrids had fewer morphological abnormalities than did diploid hybrids, possibly because triploid hybrids had two sets of chromosomes from the same species. Received March 5, 1983 Accepted August 8, 1983

Ctenopharyngodon idella (grass carp) and Aristichthys nobilis (bighead carp) have a diploid chromosome number of 48 with no acrocentric chromosomes. The hybrid of these species is triploid with 72 chromosomes. The frequencies of metacentric and submetacentric chromosomes suggest that the hybrid receives two maternal and one paternal set of chromosomes.