Contrary to their name which suggests the fish stays in group, they are actually the solitary type. Unlike snappers which move in groups, they are intolerant of the same species or other similar fishes. Most species gather together in pairs or aggregations only for spawning. Many species are hermaphrodites, meaning that they can change their sex. They start out as females and change to male at a later stage.
There are 64 genera and approximately 521 species worldwide. Malaysia is represented by 15 genera and approximately 68 species.
There are two production systems used for the nursery stage - indoor and outdoor. The indoor system uses tank sizes of 30-50 m3 while the outdoor system uses ponds of >200 m3.
Outdoor System
Hatchery reared or wild-caught fry are nursed in tanks or hapa nets until they reach 6 cm. Hapa nets [1 x 2 x 1.5 m; -2 mm mesh] are set in tanks or ponds or inside floating net cages and stocked
Indoor System
Nursery tanks vary from 30 to 50 m3 in either semi-intensive or intensive flow-through systems. Such tanks are stocked with 3. Higher densities of over 1 000/m3 are sometimes used in flow-through or recirculation water systems. The fish are graded every 5-7 days until they reach >6 cm after 45-60 days. At this stage, fish are transferred to grow-out ponds or floating cages.
Outdoor System
Hatchery reared or wild-caught fry are nursed in tanks or hapa nets until they reach 6 cm. Hapa nets [1 x 2 x 1.5 m; -2 mm mesh] are set in tanks or ponds or inside floating net cages and stocked
Indoor System
Nursery tanks vary from 30 to 50 m3 in either semi-intensive or intensive flow-through systems. Such tanks are stocked with 3. Higher densities of over 1 000/m3 are sometimes used in flow-through or recirculation water systems. The fish are graded every 5-7 days until they reach >6 cm after 45-60 days. At this stage, fish are transferred to grow-out ponds or floating cages.
Earthen Pond systems
Ponds are prepared and fertilized. Once natural food is abundant, adult tilapia are added at a stocking density of 5 000-10 000/ha to produce fingerlings to serve as live prey for the groupers. Grouper fingerlings (~6 cm TL) are added at 5 000-10 000/ha at least a month after the release of adult tilapia. Sorting and grading of the fingerlings is carried out weekly to prevent cannibalism and to minimize competition for space and food. If tilapia fingerlings are not abundant, supplementary feeding is carried out using chopped fish at 5 per cent BW/day, half early in the morning and the rest late in the afternoon. When the fish weigh about 200 g, feeding is reduced to once daily with fresh or frozen chopped fish at 5 per cent BW or with pellets at 2 per cent BW. 20-50 per cent water exchange takes advantage of spring tides or pumped water from reservoirs and is carried out at least twice/week. Paddlewheel aerators are used when DO2 falls below 4 ppm. Water quality is maintained at pH 7.5-8.3, 25-32 °C, 20-35 ‰, 4-8 ppm DO2; 2-N) and 3-N.
Floating Net Cage Systems
Net cages (8 mm mesh) are used for 2-10 cm fingerlings; 25 mm mesh is used for larger fish. Grouper fingerlings are stocked at 15-20/m3. Grading is carried out at least once a month. Fish are fed with appropriate fresh or frozen chopped fish daily at 10 per cent BW or with pelleted feeds 3 per cent BW, half early in the morning and half late in the afternoon. 0.5 per cent vitamin and mineral premix is added to the properly thawed trash fish before feeding. Floating net cages should be moved to a new site every 2-3 years of culture to allow deteriorating bottom conditions to recover. The duration of culture in the grow-out phase is 4-7 months, depending on the preferred size at harvest.
Ponds are prepared and fertilized. Once natural food is abundant, adult tilapia are added at a stocking density of 5 000-10 000/ha to produce fingerlings to serve as live prey for the groupers. Grouper fingerlings (~6 cm TL) are added at 5 000-10 000/ha at least a month after the release of adult tilapia. Sorting and grading of the fingerlings is carried out weekly to prevent cannibalism and to minimize competition for space and food. If tilapia fingerlings are not abundant, supplementary feeding is carried out using chopped fish at 5 per cent BW/day, half early in the morning and the rest late in the afternoon. When the fish weigh about 200 g, feeding is reduced to once daily with fresh or frozen chopped fish at 5 per cent BW or with pellets at 2 per cent BW. 20-50 per cent water exchange takes advantage of spring tides or pumped water from reservoirs and is carried out at least twice/week. Paddlewheel aerators are used when DO2 falls below 4 ppm. Water quality is maintained at pH 7.5-8.3, 25-32 °C, 20-35 ‰, 4-8 ppm DO2; 2-N) and 3-N.
Floating Net Cage Systems
Net cages (8 mm mesh) are used for 2-10 cm fingerlings; 25 mm mesh is used for larger fish. Grouper fingerlings are stocked at 15-20/m3. Grading is carried out at least once a month. Fish are fed with appropriate fresh or frozen chopped fish daily at 10 per cent BW or with pelleted feeds 3 per cent BW, half early in the morning and half late in the afternoon. 0.5 per cent vitamin and mineral premix is added to the properly thawed trash fish before feeding. Floating net cages should be moved to a new site every 2-3 years of culture to allow deteriorating bottom conditions to recover. The duration of culture in the grow-out phase is 4-7 months, depending on the preferred size at harvest.
3.)Life Cycle of Red Grouper
Juveniles live in shallow-water nearshore hardbottom reefs where they remain for 4 to 5 years. Adults occur in rock formations and crevices of limestone reef as deep as 300 feet. They grow slowly, reaching a maximum weight of about 50 pounds in their 29 years of life. Females reach sexual maturity between the ages of 4 and 6 years when they start to pair spawn with males. They release egg and sperm into the water column and the resultant larvae are pelagic, floating in the plankton for up to 45 d before settling out in hardbottom habitat inshore. As an overlay on this life cycle are life histories and behaviors that they also share. They are slow to mature and have complex social systems that provide cues for sex change. They also exhibit a high degree of site fidelity within their home ranges and to spawning aggregation sites where they are easy to capture, particularly with the remarkable improvements in navigational gear that allows targeting specific spawning locations.
Sex change in groupers is a one-way street, from female to male. For Gag (Mycteroperca microlepis)-- one of the more important species fished in the eastern Gulf of Mexico—the period in which sex change is initiated is brief, occurring only during the late winter or early spring. At other times, males and females are separated, with males staying offshore on spawning sites while females move to shallower water. All of the reproduction in the population takes place in the brief time the sexes co-occur. So do all the cues for sex change. If there are two few males, then dominant females will change sex so that by the following spawning season, more males are available.
This combination of traits make them highly vulnerable to exploitation and habitat loss. There are currently no management plans in effect to adequately protect either their social structure or their nursery habitat. While marine reserves have proved an effective tool for protecting offshore spawning grounds, they have not been applied to nursery habitat which remains vulnerable to the effects of eutrophication, development, and industrial contamination.
Lifecycle of grouper
Statistic that shows the production of grouper fish in Malaysia
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