It might be expensive to integrate broodstock with hatchery; hence, hatchery operators may opt to buy milkfish eggs from broodstock operators like SEAFDEC/AQD. This distinction between egg suppliers and fry suppliers is what make Taiwan’s milkfish industry very successful because the risks are spread among sectors of the industry. Filipino entrepreneurs are enjoined to do the same.
Eggs are hatched, raised, and then sold at day 21 or older. Natural food (Chlorella, Brachionus, Artemia) are fed to the larvae, enriching the rotifer and Artemia in particular with highly unsaturated fatty acids (HUFA) and Vitamin C. The SEAFDEC/AQD-formulated larval feed may be given in combination with natural food from day 3-5 until harvest. Water change, cleaning tanks, frequent monitoring of stock and support systems like aeration are part of the hatchery routine.
|(1) A shrimp hatchery may be slightly modified by adding algal and rotifer tanks. A volume ratio of 1 ton larval rearing tank to 3 tons algal-rotifer tanks is recommended.
(2) Natural food production must start at least two weeks before the hatchery receives eggs or larvae. To culture Chlorella, start with a 1-liter starter culture in 20 liters of seawater. Fertilize with ammonium phosphate 16-20-0 and urea 46-0-0 both at 15 mg per liter plus ammonium sulfate 21-0-0 at 100 mg per liter. Aerate, and wait for the algal population to reach its peak density, usually in 3-4 days. Then add 70 liters of water. Fertilize. Continue scaling-up the algae culture until you have a 9-ton outdoor tank seeded with 1000 liters of Chlorella. This will probably take 24 days.
(3) Start the mass culture of Brachionus by directly seeding concentrated culture into the 9-ton Chlorella tank. Brachionus peaks in density in 3-4 days. Harvest using a 60-micron filter bag. Note that Brachionus is scaled-up the same way as algae, starting with 10-liter cultures and using Chlorella as feed.
(4) When the natural food is ready, bring in the milkfish eggs. Acclimate then stock at 300 eggs per liter for optimum hatching which takes place in 14 to 16 hours.
(5) Prepare the rearing tanks by seeding 1 liter “greenwater” (Chlorella at its peak density) for every 30 liters of seawater. Stock 30 larvae per liter.
(6) Maintain a green to light green color of seawater throughout the hatchery run. Make sure to maintain 10-15 Brachionus per ml for the first 15 days; then reduce this to 0.5 per ml until harvest. Enriched Artemia is added to the diet in lieu of more Brachionus. About 0.5 Artemia per ml is maintained from day 15 to 17, then increase to 1 per ml onwards.
(7) To enrich Artemia, feed first with HUFA booster diets with Vitamin C supplementation (available commercially) before giving to milkfish fry. Or, feed Artemia with microalgae high in HUFA.
(8) SEAFDEC/AQD formulated diet may also be given in lieu of the expensive Artemia, at 12.5 g per ton per day, from day 15 to 25.
(9) Clean rearing tanks daily by siphoning debris out of the tank bottom; change 30% of the water from day 1 to day 15, then 50-70% until harvest.
(10) Harvest when you have buyers on day 21. Drain tanks to about a foot of water. Scoop out fry and place in plastic basins. Pack larvae in double-layered oxygenated plastic bags at 300 fry per liter.
(11) If a pond is available, the hatchery operator can nurse the hatchery-reared fry for two weeks with minimal expenses (fry thrive on naturally grown food organisms), and double the selling price of the milkfish fry.
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