WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2017 43 (CONTINUED ON PAGE 44) 1-DAH. Algal cell density is maintained at 300-400 x 103 cells/ mL. Nauplii of Acartia sp. and SS type rotifers are introduce at 2-DAH (afternoon) when larvae have partially absorbed their yolk. Acartia sp. density in the larval rearing tanks should be maintained at 0.1/mL while SS-type rotifer density should be maintained at 5-7/mL through 5-DAH . The availability of copepods seems to be especially crucial for rearing groupers that require very small prey at first feeding such as coral trout and mouse groupers. Small (S-type) rotifer are then introduced at 8-10/ mL, with density gradually decreased to 25-DAH as the rate of rotifer consumption by larvae increases. From 15-DAH onward, a commercially formulated diet with particle size of 200-400 µm is used. The feed size is gradually increased to 400-800 µm from day 35-DAH to 45-DAH. From 18-DAH onward, newly hatched Artemia nauplii are also introduced at 0.2-0.5/mL. Before introduction to larval rearing tanks, rotifers and Artemia are enriched with a commercially available HUFA booster. When larvae are fed artificial diets and Artemia, 20-50 percent of the larval-rearing water is changed daily. At 35-DAH, a 100 percent daily exchange rate is applied to avoid water quality problems. After 45-DAH, nearly all of the larvae of the eight species of grouper studied metamorphosed. The rearing protocol presented in Figure 1 is fit for all grouper species, with minor modification (Sugama et al. 1999, Liao et al. 2001, Sugama et al. 2001, Sim et al. 2005, Sugama et al. 2008, Sugama et al. 2009, Sugama et al. 2012). To increase success, greater attention is needed to produce specific pathogen free (SPF) seeds, including broodstock selection, live food production, and facilities that guarantee diseases prevention like VNN and Iridovirus infection. Hybridization Genetic improvement of grouper is important for developing disease resistance and producing strains with a high growth rate. At GRIM, research on hybridization has been undertaken to improve seed quality. E. lanceolatus grows significantly faster than E. fuscoguttatus. GRIM experience spawning E. lanceolatus in captivity has been a failure, but it is easy to get milt of mature males by stripping. Therefore, crossing male E. lanceolatus and female E. fuscoguttatus has been done to increase growth rate. Similar hybrids are also done between male E. polyphekadion and female E. fuscoguttatus. E. polyphekadion is more resistant to environmental stresses and diseases compare to E. fuscoguttatus in hatchery conditions (James et al. 1999). Therefore, crossing is necessary to increase growth rate and disease resistance. Larval development of E. lanceolatus × E. fuscoguttatus and E polyphekadion × E. fusoguttatus hybrids is normal (Ismi et al. 2013). The growth rate of E. lanceolatus × E. fuscoguttatus hybrids is greater than E. fuscoguttatus and less than E. lanceolatus. The hybrid between E. polyphekadion and E. fuscogutatus is more resistant to diseases and environmental stress compared to both parents (Sugama et al. 2014). Nursery Culture Grouper juveniles harvested from larval rearing tanks are too small (total length of 2.0-2.9 cm) and too weak for sea cage culture. Nursery culture can be done in indoor or outdoor tanks to grow juveniles to a commercial size of 8-10 cm (Fig. 2). When juveniles are stocked into nursery tanks, they usually gather near drain filters and then settle to the bottom during the first few days. Therefore, tanks with volumes of 5-10 m3 are suggested for nursery culture because these sizes are easy to manage. A stocking density of 500 juveniles/m3 is suitable (Sim et al. 2005). Nursery culture in floating cages may be possible, but grouper juveniles are very sensitive to physical disturbances such as wind and waves. Juveniles can be fed small shrimp and minced or chopped trash fish. Juveniles grown in sea cages are fed trash fish until they reach market size. Those fed with dry pellets must be well trained by feeding on artificial diets during nursery culture. There are FIGURE 1. Larval rearing protocol for groupers. Feeding Regime Nannochloropsis SS-type rotifer (5–7/ml) S-type rotifer (8–10/ml) Acartia sp, (0.5/ml) Artemia (0.2–0.5 ind./ml) Artificial Diet Size 200–400 µm Size 400–800 µm Virus check by PCR Water management Water exchange (%) 10 20 50 Flow-through Siphoning Days After Hatching (DAH) 0 5 10 15 20 25 30 35 40 45
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