The seabass can be induced to spawn in captivity either by hormone-inducing or by natural spawning. Circular tanks of 112-t capacity, 8.5 m diameter and 2 m depth, are used for seabass spawning activities at Sg. Merbok hatchery, Kuala Muda, Pantai Merdeka, Kedah. About one month before spawning season, the broodstock is transferred into the spawning tank. Twenty broodstock are kept in each 112-t tank with a male:female ratio of 1:1. Due to handling during the transfer, the fish will refrain from eating for one to two days.
To maintain good quality water in the spawning tank, periodic draining and refilling of water are necessary. Normally 50 percent of the total volume of water is changed every day. However, to ensure that the spawning tanks have the desirable water quality, the installation of a jet spray head and aeration system in the tank are preferred. The suitable ranges of water quality required in spawning tank are given in Table 2. The broodstocks are fed with trash fish once a day at 1 percent body weight. The excess food which falls to the bottom of the tank must be removed. During the process of induced spawning, unnecessary disturbance of the broodstocks should be avoided.
If the water environment in the spawning tank is suitable, the fish will respond well. The female gradually appears with swollen abdomen, swimming awkwardly. Approximately 1–2 weeks before spawning, the female fish separates from the school and reduces feeding activity. The male fish continues eating normally, schools and swims actively.
