During the spawning season the female broodstock in the ponds or cages with stage IV-V oocysts could be induced to ovulate by injection of hormones. Normally 50 IU of human chorionic gonadotropin (HCG) plus 0.5–1 dose of pituitary gland (PG) is the appropriate dose for the first injection to induce ovulation. The second dose 100–200 IU of HCG plus 1.5–2 doses of PG is applied after 12 hours. The fish will spawn in the spawning tank within 10 to 12 hours after the second injection. An overdose of HCG may result in fattening of the fish, causing regression of the female's ovaries. In the male (stage IV-V) milt formation can also be stimulated by injection of 0.5 dose of PG plus 25–50 IU HCG. Maneewongsa (1982) showed that seabass weighing about 5 kg, having been injected a first dose (3 000 IU HCG + 2 dose of PG) at 09.45 h, and followed by second dose (3 500 IU HCG+ 4 doses of PG) at 21.45 h, will be ready to spawn about midnight.
