Characterization of molecular variants of GnRH, induction of spermiation and sex reversal using salmon GnRH-A and domperidone in the protogynous diandric fish, Synbranchus marmoratus Bloch, (Teleostei, Synbranchidae)

Abstract

This paper studies the molecular variants of gonadotropin-releasing hormone (GnRH) present in the brain of the protogynous swamp eel, Synbranchus marmoratus, and the effects of the administration of salmon GnRH analogue (sGnRH-A) and the dopamine receptor antagonist, domperidone (DOM) on final maturation and gamete release in this species. Evidence for the presence of two GnRH variants, sGnRH and cIIGnRH were obtained by reverse phase high-pressure liquid chromatography (RP-HPLC) and radioimmunoassay with different antisera. The effects of treatment with sGnRH-A+DOM were checked by three ways: oocyte and milt release by stripping, histological analysis of the gonadal tissue, and androgen serum levels at different times throughout the experiment. In males, spermiation was induced after three weeks of treatment. In the female group, sGnRH-A+DOM did not induce ovulation at the end of the experiment. Histological analysis of the gonads from the female group showed evidence of sex reversal. All the treated fish had elevated androgen serum levels from the third week, with respect to control fish. In all cases, serum estradiol levels were undetectable. These results suggest that treatment with sGnRH analog and DOM induce sex reversal in female and spermiation in males.