Effects of GnRH-a on the ovarian maturation of blue tang fish (Paracanthurus hepatus Linnaeus, 1776)

Abstract

The effects of gonadotropin-releasing hormone – analogue (GnRH-a) injection on the ovarian maturation and steroid hormone level of blue tang (Paracanthurus hepatus) females were investigated. Pre-matured blue tang females were injected with GnRH-a at dosages of 150, 200 and 250 μg/kg body weight and were then observed for fluctuation of steroid hormone levels, including testosterone (T), estradiol (E2) and 17α,20β-dihydroxy-4-pregnen-3-one (DHP) in plasma and ovary after 2 and 7 days. Plasma T level was not significantly different among the treated groups at sampling times. However, the ovarian T levels in the fish injected with 200 and 250 μg/kg GnRH-a were higher than that of the non- administered GnRH-a and fish injected with 150 μg/kg after two days (P < 0.05). After seven days of the administration, the ovarian T level was lowest in the fish without GnRH-a injection and highest in the fish injected with 250 μg/kg (P < 0.05). The plasma and ovarian E2 levels were higher (P < 0.05) in the fish injected with 200 and 250 μg/kg of GnRH-a than in the control fish after 2 and 7 days of injection. Both the plasma and ovarian DHP levels in GnRH-a injected fish were significantly (P < 0.05) increased after day 2 and was highest in the fish injected with 250 μg/kg (P < 0.05). After 7 days of injection, the plasma and ovarian DHP levels remained higher in the GnRH-a injected fish than in the controlled group (P < 0.05). There was no difference in DHP levels among the GnRH-a-treated groups. The results indicate that the dosage of 200 µg/kg of GnRH-a is appropriate for inducing maturation of the blue tang fish.