Culture systems - grouper

There are many different systems used for the culture of groupers worldwide, although there appears to be an agreed set of stages: nursery, transition, and on-growing. Grouper “seed” has to be nursed before being cultured to marketable size.

The nursery stage is reared either in tanks, net cages, and hapas (nylon netting enclosures), or in earthen ponds. Grading is a prerequisite to minimize cannibalism, especially in the nursery and early grow-out stages. After nursing, there are two main systems used for on-growing: pond culture or cage culture. The stocking density and rearing conditions in both nursery and grow-out phases vary, depending on the site, the fish sizes, and the grouper species cultured.
Wild fry (2.5-7.2 cm) or fingerlings (7.5-12 cm) may initially be held in tanks or net cages or earthen ponds for a month or more (nursing period) after catching. The density may range from 100 to 150 fish/m2, e.g. a net of 2 x 2 x 2 m would hold 400-600 fingerlings. Sorting is undertaken every week, and stock sampling every 15 days. Groupers are normally retained in the nursery until they reach about 16 cm, when they are thinned out and transferred to transition nets (5 x 5 x 5 m) that each hold 1 100 fish. The fish are finally transferred to production nets after 2-3 months.

Floating cages are often constructed from bamboo poles and polyethylene netting material (25-50 mm mesh size). The net cage is formed by two types of panels: 4 side panels forming the walls, and one bottom panel. The net is secured to the raft structure (bamboo poles) by ropes. Ropes are also used to lash the bamboo poles together. Buoyancy is provided by empty plastic containers attached to the bamboo frames (www.seafdeec.org.ph). According to Agbayani (2002), net cages come in several sizes (3 x 3 x 2.5 m; 4 x 4 x 2.5 m; 10 x 10 x 3 m); the mesh size ranges from 10 mm to 35 mm. The optimum stocking density averages 120 fish/m3. Growth to marketable size (600-800 g) takes approximately 8 months, with survival rates of 50% or less (Leong 1997). Groupers can grow to 600 g in 12 months, to 1 kg within 18 months, and to 2 kg within 24 months (Tucker 1999).
A summary of the conditions for grouper culture is presented in Table 39 (www.seafdeec.org.ph). For brackish water culture, ponds are 800 to 1 600 m2, or from 6 400 m2 to 12 800 m2. The pond depth should at least be 1-2 m, with a level pond bottom to allow for easy harvest.
Table 39. Summary of the characteristics of grouper culture systems