عنوان مقاله [English]
During a six-month study (from August to January, 2002) ovarian development stages of grey mullete (Mugil cephalus) were histologically studied in the rearing ponds of South Caspian Sea (Gomishan). Different stages of oocyte development (nucleus changes, oocyte diameter and forming of yolk vesicle, yolk granules and lipid droplets) was surveyed. Hormonal treatment was accomplished to induc final maturation and spawning in captive females. In this study, 12 females were injected with a priming injection of carp pituitary hormone (CPH) at a dosage of 20 mg/kg body weight followed 24 h later with a resolving injection of HCG at a dosage of 20 Iu/100gr body weight and CPH at a dosage of 20 mg/kg body weight. Another three fish received saline injections as controls. During hormonally induced spawning, 8 mullet spawned. All fish were bled and checked for ovulation 0, 24, 30 and 48 hours post injection. Plasma level of estradiol-17β (E2), testosterone (T) and 17α-hydroxyprogestrone (17-OHP) were determined by radioimmunoassay. Steroid profiles of spawned fishes were similar. Plasma E2 and then T levels dramatically increased for 30h after first injection. A surge of 17-OHP was observed when E2 and T level decreased. These dramatic changes were coincident with oocyte undergoing hydration, germinal vesicle breakdown and ovulation. The oocyte of spawned mullets in the onset of experiment, were completed vitellogenesis. The fluxes of sex steroids of unspawned females had a delay comparing with spawned mullets. The oocyte of these fishes at the first injection had not completed the vitellogenesis. None of the three females in the control group had significant changes in maturing stages of oocyte and levels of sex steroids. According to the results, stage I, II, III and IV of ovary maturation of grey mullet occurred in July, August, September and October, respectively. The results indicated fishes were ready for hormonal induction from November. Morover, E2, T, and 17-OHP were introduced as important steroids in developing and final maturation of grey mullet oocyte under the influence of gondotropin.