Tiny grouper fry which are newly caught from the wild are very delicate and sensitive to changes in water conditions (e.g. water salinity, turbidity, temperature, DO), hence, stocking them directly into the nursery ponds or net cages will result to high mortalities. Therefore, it is necessary for tiny groupers (2-3 cm body length) to first be conditioned in plastic or concrete tanks for a month under controlled environmental conditions.
Upon arrival to the site , newly caught wild grouper fry are first sterilized in 10-20% formalin solution for about 15-20 minutes to free the fry of any bacterial or parasite infection. After sterilization, the fry are stocked in aerated tanks filled with live small fish and crustaceans (e.g. fish larvae, Acetes, Artemia) and insect larvae at least three times a day of 0600, 1200 and 1800h respectively (Table 2).
Before feeding the fish, tanks are changed with new sea water and cleaned of dirt, fish faeces and uneaten food. The fry must be sorted every 2 weeks by separating the big ones (shooters) from the small ones to avoid cannibalism. After a month, the surviving grouper juveniles can now be transferred to the nursery net cages.
Sort healthy and conditioned grouper juveniles (3-5 body length) and stock in nursery net cages at a stocking rate of 60-100 fish per cu.m. The nursery net cages should have a 2-5mm mesh size and measure 2m x 2m x 1m, submerged about 80 cm below the waterline. For safety reasons, it is advisable to cover the net cages with nets. Feed the juvenile groupers to satiation three times daily at 0600, 1200 and 1800 h respectively.
During the first month, the fish are fed with live small fish, crustaceans and insect larvae. In the second month, the fish are weaned with finely chopped trash fish and small shrimp ( Table 2). To prevent cannibalism, the fish are sorted every 2 weeks by manually separating the
smaller ones in another net cage.
Install a 50-watt incandescent lamp (hover type) inside the cages, about 0.5 m above the water line, at night to attract live food such as mysids, copepods and other smaller fishes.
After 2 months in the nursery net cages, the fingerlings (8-10 cm body length) are transferred into the grow-out net cages.
The grow-out stage can be undertaken in net cages measuring 2m x 2m x 1m, 3m x 3m x 1.5 m and 5m x 5m x 2m using a G net or PE knotted net with a 2-3 cm mesh size (Table 1). The stocking rate in the grow-out net cage is varied depending on the size of grouper (Table 3). Table 3. Recommended Stocking rate of grouper in grow-out net cages.
Table 3 : Initial Body Weight = Fish Body Lenght = Stocking Rate
- 20-30g = 8-12cm = 50-60 cbm
- 200-250g = 17-22cm = 30-40 cbm
- 400g above = 25-30cm = 20-30 cbm
During the grow-out operation, the stocking rate is reduced when the fish reach the given body weight. Give trash fish at a rate of 5 % of the average body weight every 2 days.
- Take a few samples of the stock every 15 days to determine feed requirement and growth rate of grouper stock. Scoop out 10-15 samples and measure the weight of each sample. The average body weight will be used in determining the feed requirement bimonthly. Inspect nets for tears or breaks.
- Clean/remove dirt, debris and fouling organism attached to the nets
- Repair or replace damaged nets
source: DA – BFAR RF8, Tacloban City