Potential for bias in using hybrids between common carp (Cyprinus carpio) and goldfish (Carassius auratus) in endocrine studies: a first report of hybrids in Lake Mead, Nevada, U.S.A
During a 2008 study to assess endocrine and reproductive health of common carp ( Cyprinus carpio ) in Lake Mead, Nevada (U.S.A.) we identified two fish, one male and one female, as hybrids with goldfish ( Carassius auratus ) based on morphology, lateral line scale count, and lack of anterior barbels. Gross examination of the female hybrid ovaries indicated presence of vitellogenic ovarian follicles; whereas histological evaluation of the male hybrid testes showed lobule-like structures with open lumens but without germ cells, suggesting it was sterile. Because common carp/goldfish hybrids are more susceptible to gonadal tumors and may have different endocrine profiles than common carp, researchers using common carp as a model for endocrine/reproductive studies should be aware of the possible presence of hybrids.