STUDIES ON THE REPRODUCTIVE BIOLOGY OF GONADAL TUMOUR-BEARING CARP-GOLDFISH HYBRIDS.

摘要

The hybrids of carp (Cyprinus carpio) and goldfish (Carassius auratus) collected from the lower Great Lakes between 1978 and 1981 exhibited epizootics of gonadal neoplasms which were rare in the parental species. Historical evidence has implicated an environmental etiology for these tumours. Electophoretic analysis of tissue proteins and discriminant analysis of morphometric and meristic data indicated that the hybrids were a homogeneous group, intermediate to the parentals and of the F(,1) generation providing indirect evidence of hybrid sterility.;The pituitary glands of hybrids were hypertrophied due to a hyperplasia of the proximal pars distalis gonadotrops and contained more immunologically active gonadotropin (GtH) than sympatric carp. Moreover, heterologous gonad bioassays indicated that the hybrid GtH had biological activity. Serum GtH levels in hybrids were as high or higher than levels in sympatric carp, indicating that the hybrids release GtH into the blood.;Serum testosterone levels in male and female carp and non-tumoured hybrids were similar. Serum 11-ketotestosterone levels were higher in males but carp and non-tumoured hybrids exhibited similar values. Serum 17B-estradiol levels were highest in female carp while levels in all hybrid groups approximated those of male carp. Hybrids with primitive stromal tumours had the highest levels of the two androgens which may indicate an androgenic function for the proliferating cell type. Absent or retarded steroidogenesis could not be supported as the cause of the hypophyseal hyperplasia in the hybrids.;Theories as to why the hybrids are more susceptible to oncogenic transformations than the parentals are discussed, as is the use of the hybrid as a sentinel for environmental contamination and as a model for some events in teleost reproductive endocrinology.;The gonadal histology of male and female carp captured for this study was typical of a successfully reproducing population but hybrids appeared to be sterile. In male hybrids meiosis was often completed but spermatids usually degenerated in early spermiogenesis. In female hybrids vitellogenesis was frequently completed but there was no evidence of final maturation or ovulation. Proliferations of undifferentiated germ cells and stromal cells were evident in the tumour nodules of both the male and female hybrids.