Effects of Exogenous Hormones on Spawning Performances, Serum Gonadotropin and Sex Steroid Hormone in Manchurian Trout (Brachymystax lenok) during Sexual Maturation

The objective of this study was to investigate the effects of salmon gonadotropin releasing hormone analog (S-GnRH-A) and human chorionic gonadotropin (HCG) on the serum levels of gonadotropins (GtHs) and sex steroid hormones in Manchurian trout during sexual maturity. Females in the treatment group were injected with 20 µg/kg S-GnRH-A and 400 IU/kg HCG, whilst males were injected with half the amount. Blood samples were collected at 0, 5, 10, and 20 days post injection (dpi). The results showed an increase in female follicle-stimulating hormone (FSH) levels in the treatment group at 5 dpi, and from 5 dpi onwards, a difference was observed between the groups, with higher FSH levels in the treatment group compared to the control group. In males, FSH levels showed group differences at only 5 dpi (p < 0.05) and were higher in the treatment group. In females, luteinizing hormone (LH) peaked at 10 dpi in the treatment group, and there were differences between the two groups at 10 dpi and 20 dpi. In males, LH was significantly higher in the treatment group than in the control group at 5 dpi and 10 dpi (p < 0.05). In females, estradiol (E2) was significantly higher in the treatment group than in the control group at 5 dpi and 10 dpi (p < 0.05), whereas in males, the difference between the two groups was only observed at 5 dpi (p < 0.05). The female testosterone (T) level in the treatment group was significantly higher than that of the control group at 5 dpi and 10 dpi (p < 0.05), while T levels were significantly higher in the male treatment group than in the control group at 5 dpi (p < 0.05). The level of 17α–hydroxyprogesterone (17α-OHP) in the females of the treatment group was significantly higher than that of the control group at 5 dpi and 10 dpi (p < 0.05), and 17α-OHP levels were significantly higher in the male treatment group than in the control group at 10 and 20 dpi (p < 0.05). The fish were successfully spawned after S-GnRH-A and HCG injections, and brood amount, fertilization rate, and hatching rate were significantly increased (p < 0.05). This study provides a framework for a better understanding of the mechanisms of exogenous hormone-mediated control of reproduction in Manchurian trout.