Effects of human chorionic gonadotropin and gonadotropin releasing hormone analogue on plasma steroid hormones and spawning performances in golden rabbitfish Siganus guttatus

Abstract

In this experiment, golden rabbitfish (Siganus guttatus) were allocated between three treatment groups. The fish were injected with saline, human chorionic gonadotropin (hCG) and D‐Ala6, Pro9‐Net‐mGnRH. After injection, in 6 hr intervals, blood plasma samples were collected for steroid hormone (testosterone [T] in males and estradiol‐17β [E2] in females) using enzyme immune assay (EIA). In male fish, T levels significantly increased and reached 170 and 650 pg/ml for hCG and D‐Ala6, Pro9‐Net‐mGnRH treatments, respectively. Then T levels slightly decreased until 24 hr post injection. There were no significant changes of T levels in saline treatment. In female fish, we found significant changes in E2 levels at 2,567 and 524 pg/ml at 12 hr post injection in hCG and D‐Ala6, Pro9‐Net‐mGnRH treatments, respectively. No significant differences of E2 levels were observed in saline group. In the second experiment, we injected 100 golden rabbitfish with both hCG and D‐Ala6, Pro9‐Net‐mGnRH. Fish spawned successfully when hCG and D‐Ala6, Pro9‐Net‐mGnRH were given individually and in combination. Latency periods were between 46–64 hr with an average fertilization rate of 70%–90% and hatching rate of 56%–74%. The embryonic duration was 16–20 hr. The saline‐injected group produced no spawning. Our findings contribute to further understanding of exogenous hormones impact on golden rabbitfish reproductive endocrinology, refining breeding protocol and implications for fish propagation.