Induced spawning of maturing milkfish (Chanos chanos Forsskal) with gonadotropin-releasing hormone (GnRH) analogues administered in various ways

The response of mature female captive milkfish to mammalian and salmon gonadotropin-releasing hormone analogues (mGnRH-A and sGnRH-A) was investigated. Prior to spawning, six groups of three females received (1) 10–16 μg mGnRH-A from an osmotic pump implanted intraperitoneally (IP); (2) 100 μg mGnRH-A from a cholesterol/cellulose pellet implanted IP; (3) 10 μg/kg mGnRH-A as an intramuscular (IM) injection; (4) 10–16 μg sGnRH-A from an osmotic pump implanted IP; (5) 100 μg sGnRH-A from a cholesterol/cellulose pellet implanted IP, and (6) a cholesterol/cellulose pellet without analogue implanted IP. The most effective treatment was 100 μg sGnRH-A/fish given in a cholesterol/cellulose pellet; all ( 3 3 ) of the fish spawned. However, mGnRH-A was more effective ( 2 3 ) compared with sGnRH-A ( 1 3 ) if osmotic pumps were used to administer GnRH-A. If the dose and method of administration were not considered, then the salmon and mammalian GnRH analogues were equally effective (62–67%) for induction of ovulation and natural spawning in milkfish. Gonads of control fish regressed. At the doses tested, injections or pellet implantations were more effective compared with osmotic pumps. All pellet-implanted and injected females responded to treatment and 75% ( 6 8 ) spawned; half ( 3 6 ) of the pump-implanted females spawned. Spawning occurred from 18 to 36 h after treatment.