Seasonal changes in serum gonadotropin, testosterone, 11-ketotestosterone, and estradiol-17 beta levels and their relation to tumor burden in gonadal tumor-bearing carp x goldfish hybrids in the Great Lakes.

The hybrids of carp (Cyprinus carpio) and goldfish (Carassius auratus) collected from the lower Great Lakes between 1978 and 1981 exhibited a high frequency of gonadal neoplasms and apparent sterility, conditions which were rare in the parental species. A pronounced hyperplasia of gonadotropic cells in hybrids resulted in the accumulation of large stores of biologically active gonadotropin (GtH) in the pituitary gland. Serum GtH levels were generally higher in hybrids than in carp collected from the same areas, but seasonal trends were similar for both species. Among hybrids, tumored individuals had higher serum GtH levels than nontumored individuals. Serum levels and seasonal trends for testosterone (T), 11- and ketotestosterone (11-KT), and estradiol-17 beta (E2) were, for the most part, similar when carp and nontumored hybrids of the same gender were compared. Serum levels of T and 11-KT (but not E2) were generally higher in tumored hybrids when compared to nontumored individuals. High serum steroid levels were related to a specific tumor type, possibly of Sertoli cell origin. Although the etiology of the gonadal tumors is not yet known, the serum levels of gonadal steroids in hybrids make it unlikely that a lack of steroidal feedback is responsible for the gonadotrop hyperplasia.