Effect of chicken gonadotropin-releasing hormone (cGnRH-II) on plasma steroid hormone, maturation and ovulation in African catfish, Clarias gariepinus (Burchell)
AbstractNowadays, many studies on the effects of native GnRHs and various agonists have been evaluated on the spawning of African catfish, Clarias gariepinus. For the current study, three experiments have been
conducted to determine the effectiveness of chicken gonadotropin-releasing hormone II (cGnRH-II) in stimulation of maturation and ovulation of African catfish. The first experiment concerned the graded
dosage treatment; the second experiment was designed specifically to determine the response of dopamine inhibitor to accelerate the maturation process. Finally the third experiment was carried out to compare the effectiveness of cGnRH-II against leutinising hormone releasing-hormone analogue (LHRHa) and salmon gonadotropin-releasing hormone analogue (sGnRHa) in inducing maturation and ovulation. Plasma steroid levels (17ß-estradiol (E2) and testosterone) were determined and germinal
vesicle (GV) was observed prior to hormone administration at (0), 6, 12 and 24 h post injection. From the first experiment, cGnRH-II 200 g/kg was found to be effective to induce ovulation in African catfish.
100% ovulation was also observed for the fish treated with cGnRH-II 200 g/kg with the combination of pimozide based on the second experiment. Finally in the third experiment, sGnRHa was proven to be more efficient compared to cGnRH-II, only 20 g/kg was administered intramuscularly in single injection. For the group that showed ovulation, that is cGnRH 200 g/kg alone and with the combination of pimozide and also sGnRHa, plasma level of E2 and T increased significantly with the association of
germinal vesicle migration and ultimately ovulation. The concentration reached the peaked after 12 h, then decreased dramatically at 24 h post treatment. In contrast to the non-ovulated group that is cGnRH-II 2 and 20 g/kg, the plasma level showed small increased after the injection and throughout the experiment. The present study indicates that administration of cGnRH-II is effective for sexual maturation and ovulation in African catfish.