Brief description: Seabass can easily be spawned using a hormone and its larvae reared in the hatchery with 90% survival. The only potential problem for the hatchery operator is that seabass are protandrous hermaphrodites, that is, they first mature as males then become females on their sixth year or when they are over 3 kg in size. Should egg production decrease as a result of having more female broodstock, the operator must cull and acquire younger or male broodstock.
Wild spawners may be used, or breeders raised in cages,tanks or ponds. Seabass are injected with LHRHa, and left to spawn for 2-3 consecutive days. The larvae that hatched from the eggs are fed mostly live food, Brachionus and Artemia. Because the latter is quite expensive, SEAFDEC/AQD researchers had found alternatives in cladocerans (or fleas); the freshwater species is Moina and the estuarine species is Diaphanosoma and both can be collected and raised cheaply like Brachionus.
The thing to watch out for in seabass hatchery, in addition to the routine activities, is regular sorting and size-grading of fry to prevent cannibalism. A three-layered sorter box can be easily and cheaply made.
(1) Procure seabass breeders (2-8 kg) at a sex ratio of 1:2 female:male. Get egg samples by cannulation and make sure average egg diameter is at least 0.4 mm; males should give out milt. Inject with a fresh solution of LHRHa at 20-100 micrograms per kg of fish. Put them back to spawning tank or cage. Seabass will spawn on the second night after injection.
(2) Collect and incubate eggs in tanks at 1,200 eggs per liter. These hatch in about 14 hours.
(3) Stock 30 seabass larvae per liter but reduce this density to 15 per li on day 10, then to 6 per li on day 21.
(4) Add and maintain 1-3 x 105 Chlorella cells per ml to maintain water quality and to serve as food to rotifers; this is the same principle as in milkfish hatchery operations. It is best to introduce live food before the seabass larvae begin feeding 50 hours after hatching.
(5) Feed daily ~ 15-20 Brachionus per ml on the first 12 days, 0.5 to 2 Brachionus and Artemia per ml on days 12 to 15, and finally, 5-10 Artemia per ml afterwards until harvest. The cladocerans Moina and Diaphanosoma can be fed to day 15 larvae as partial replacement to Artemia. Being live feed, there is no danger in feeding these to satiation.
(6) Sort and size-grade every week such that there is not more than 30% size difference in one tank. Rear the shooters separately; they usually show after Artemia feeding.
(7) Make sure the rearing tanks are cleaned daily and the water changed.
(8) Harvest after 26 days of rearing.
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