Hormonal induction of precocious sex reversal in the ricefield eel, Monopterus albus.
Ricefield eels were given twice weekly injections for 9 weeks of a salmon GnRH analogue (sGnRH-A; 0.1 μg/kg body weight), the dopamine receptor antagonist domperidone (5 μg/kg), sGnRH-A + domperidone, carp pituitary homogenate (CPH) or saline (controls). Treatment with sGnRH-A alone or in combination with domperidone induced precocious sex reversal of ♀♀. 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. The sex-reversed fish had increased serum testosterone levels and depressed oestradiol-17β levels, similar to the hormone pattern of ♂♂ which had undergone natural sex reversal. Domperidone alone did not induce sex reversal and tended to inhibit ovarian development. CPH also did not initiate sex reversal but stimulated ovarian development and increased serum oestradiol-17β levels. The results suggest that the hypothalamo-hypophyseal system is important in the initiation of sex reversal in ricefield eels.