Effects of Steroid Hormones on the Sex Differentiation in a Cichlid Fish, Tilapia zillii

Abstract

The present investigation deals with the effects of steroid hormones on the sex differentiation in T. zillii. Steroid hormones used were ethinylestradiol and methyltestosterone. Oral administration of steroid hormones caused no sex reversals. Ethinylestradiol inhibited the development of spermatogenesis and the differentiation of gonad into testis. On the other hand, methyltestosterone caused an inhibitory effect on the development of oogenesis and a remarkable propagation of somatic elements of gonad. The degree of inhibitory effect was dependent on the dosage level of steroid hormones. In general, lower dosage level of ethinylestradiol caused an inhibitory effect on spermatogenesis, whereas higher dosage on gonadal differentiation. Contrary to the treatment with ethinylestradiol, methyltestosterone caused no effects on gonadal differentiation. It may be assumed that the failure to obtain a sex reversal is due to the higher dosage levels of steroid hormones used in the present investigation. © 1978, The Japanese Society of Fisheries Science. All rights reserved.