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Fisheries > Culture Fisheries > Seafishes >Seabass

Larval Rearing

The larvae and post larvae are reared at first in indoor tanks until they metamorphose into fry at about the 20th day after hatching. Larvae are stocked @ 30-40 nos./litre in fibre glass/RCC rectangular tanks of 4-5 tonne capacity. Larvae thrive on the yolk for the first 3 days. The 3-day old larvae should be fed with rotifers (Brachionus plicatilis) @ 2 nos./ml initially and gradually increased to 5 nos./ml till 8th day. From 9th day onwards, larvae should be fed with 5 nos./ml. rotifer and Artemia nauplii. Artemia nauplii density should be maintained @ 1 no./ml initially and increased to 3 nos./ml upto 15th day. From 16th day to 25th day, larvae should be exclusively fed with Artemia nauplii at a density of 4-5 nos./ml. All the feeds should be given in 4 doses at an interval of 6 hrs. After 20 days the larvae metamorphose into fry. The survival rate from hatching to fry stage is about 35-42%.

Nursery rearing

Nursery rearing of seabass fry in ponds and cages to stockable juvenile size is essential before release into the grow-out ponds. Nursery ponds may range in size from 500-2000 m2. A water depth of 50-80 cm is desirable. In a prepared nursery pond, fry of 1.0 to 2.5 cm size can be stocked @ 20-50 nos./m2. Water exchange to the extent of 30% is required daily. Fry must be fed with supplementary feed of chopped and ground fish (4-6 mm size) @ 100% of the body weight, twice a day, in the first week. The feeding rate is gradually reduced to 60% and 40% during second and third week respectively. Though seabass prefers live fish food it could be weaned to trash fish within 5-7 days. The nursery-rearing period is about 30-45 days.

On 25th day, the fry measures 1.0 cm, which should be transferred to nursery tanks in the hatchery or nursery hapas at the farm site. Fry are stocked @ 1000 nos./m3 in 4-5 tonne capacity tanks. The cooked and minced fish meat, made into small pieces of 1.5-2.5 mm, should be given as feed ad libitum during the nursery rearing. Grading (removal of shooter fish) should be done on alternative days to reduce cannibalism. In the case of rearing seabass in the hapas (2m x 2m x 1m size), fry should be stocked @ 500 nos./m2. Feeding and grading should be done as in the case of tank rearing. The expected survival rate would be 80-86% with an average size of 1.25g in 30-35 days of rearing in the tank or hapa. Nursery cage size may range from 3 m (3x1x1 m) to 10 m (5 x 2 x 1 m) with a mesh size of 1 mm. Stocking density with fry of size range 1.0 - 2.5 cm may vary from 80-100 nos./m. Feeding schedule to be followed as in pond rearing. Cages should be checked and cleaned regularly. The fry on reaching a size of 5-10 g at the end of a rearing period of 30-45 days can be stocked in the grow-out system. Usually a survival rate ranging from 50-70% could be obtained.

larval_rearing

Larval rearing tanks

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