EFFECTS OF ESTROGENS ON TILAPIA-AUREA - IMPLICATIONS FOR PRODUCTION OF MONOSEX GENETIC MALE TILAPIA

Three naturally occurring estrogens, estriol, estrone and 17-Beta estradiol, were each administered perorally at three concentrations for 3- or 5-week periods to fry of Tilapia aurea, 8-11 mm long. Estrogen treatment neither affected survival nor altered growth of fry. Post-treatment stocking in outdoor concrete tanks revealed no apparent differences in survival between hormone-treated and untreated fish after 99-148 days. Gonadal examination of treated and untreated groups after growth trials revealed no aberrant sex ratios in the groups treated with estrogen, but in all treatment groups there were significant proportions of males with a female-like urogenital papilla. Greater proportions of such 'atypical' males occurred at the higher estrogen dosage levels and in the longer treatment period. No atypical males were found in the control groups. Sexing of fish that died after treatment indicated no difference in the death rate of the sexes. Histological examination of gonads revealed no alteration of normal male and female germ cell development; pseudo-oocytes were present in both treated and untreated groups. No ovotestis condition was observed. Male and female homogamety among different tilapia species and a method for producing monosex genetic males from matings of sex-reversed brood stock are discussed. © 1979.