Ploidy of Feral Grass Carp in the Chesapeake Bay Watershed

Abstract

We examined the ploidy of feral grass carp Ctenopharyngodon idella captured from open waterways of the Chesapeake Bay watershed. Using flow cytometry, we determined the ploidy of blood and gonads (when mature ovaries or testes were present) to elaborate upon several issues associated with stocking grass carp, namely, escapism, illegal stockings, and the reproductive potential of triploid grass carp. During a 3-year period (1994–1997), ploidy was determined for 11 of 16 feral individuals, 2 of which were diploid (18%). In the survey, we detected gonadal development in one diploid female, three triploid females, and one triploid male. Flow cytometry analysis revealed multiple ploidy in the gonadal tissue of both sexes of triploids. This is the first examination of gonad ploidy in feral triploids, and we provide evidence that although some triploid grass carp may produce gametes, viable offspring would be produced only under extremely unlikely conditions.