Hormonal induction of precocious sex reversal in the ricefield eel, Monopterus albus

The present study has evaluated the effects of a salmon gonadotropin-releasing hormone analog (sGnRH-A), the dopamine receptor antagonist domperidone (DOM) and carp pituitary homogenate (CPH) on sex reversal and serum steroid levels in the ricefield eel. Treatment with sGnRH-A alone or in combination with DOM for a 9-week period induced precocious sex reversal of female to male ricefield eel. The gonads of sex-reversed fish contained functional testicular tissue with secondary spermatocytes and spermatids; some primary oocytes were present, but no secondary oocytes remained. Sex-reversed fish treated with sGnRH-A either alone or in combination with DOM had elevated serum testosterone levels and depressed 17β-estradiol levels which was comparable to the hormone pattern of males which had undergone natural sex reversal. DOM alone did not induce sex reversal but tended to inhibit ovarian development. Also treatment with CPH did not initiate sex reversal but stimulated ovarian development and increased serum 17β-estradiol levels. These results suggest that the hypothalamo-hypophyseal system may play a significant role in the initiation of sex reversal in the ricefield eel and that GnRH is a key factor in this process.