Adult Japanese parrot fish, Oplegnathus fasciatus, mature and spawn in sea pens or aquariums. But artificial induction of ovulation is necessary to get a large amount of fertilized eggs for sex control or induction of polyploidy in order to create new varieties of important species for fish culture. In the present study, maturation and ovulation were induced in Japanese parrot fish with viteliogenic oocytes by using chum salmon pituitary homogenate (5 mg/kg fish) in combination with human chorionic gonadotropin (500 IU/kg fish) given as a single intramuscular injection. A total of 160 female fish was used; hormone injections were carried out on 80 fish and the rest 80 fish were untreated (control), and they were kept with respective 50 mature male fish in each sea pen.
In the fish tested, a high maturation success was achieved one day (94%) and two days after injection (73%), and ovulations were observed in the fish sampled at 23-25 h and 52 h after injection. There were no significant differences in gonad index (GI) and mature egg number (g-1 ovary) between mature fish one day after injection and mature control fish, but GI and mature egg number in the mature fish two days after injection were significantly lower than those of mature fish one day after injection and mature control. These results suggest that one day (25-29 h) after injection is desirable for the time of stripping. The mean fertilization rate and hatching rate in the control fish just after ovulation (N=6) were 70% and 81%, respectively, but those rates in the experimental fish in the same condition (N=1) were 3% and 0%.
