Induced spawning of maturing milkfish (Chanos chanos) using human chorionic gonadotropin and mammalian and salmon gonadotropin releasing hormone analogues

Abstract

The response of maturing female milkfish to D-Ala⁶-des Gly¹⁰ mammalian GnRH ethylamide (mGnRH-A), D-Arg⁶-des Gly¹⁰ salmon GnRH ethylamide (sGnRH-A) and human chorionic gonadotropin (hCG) was investigated. The GnRH analogues and hCG were equally effective when administered by intramuscular injection at doses of 10 μg/kg and 100 μg GnRH-A/fish or 1000 IU hCG/fish. All of the females injected with HCG and 87.5% (⅞) of females injected with GnRH-A spawned. Pellet implantation of the GnRH analogues, however, was less effective based on 100 μg of pellet per fish, which provided from 20 to 36 μg of analogue per kg fish. Fish implanted with mGnRH-A or sGnRH-A showed responses which varied from oocyte hydration to spawning. Only ³⁄₇ implanted with mGnRH-A and ¹⁄₇ implanted with sGnRH-A spawned; in the latter group, the average egg diameter was 11–17% smaller at the time of treatment compared with the other treated groups. Except for one, all fish with egg diameters above 0.65 mm had hydrated/ovulated oocytes or spawned. Females which spawned had egg diameters above 0.71 mm.