44 JUNE 2017 • WORLD AQUACULTURE • WWW.WAS.ORG several types and sizes of commercial diets for grouper. Based on the results of fish nutrition research at IMRAD-Gondol, the nutrient requirements for juvenile groupers are 47-54 percent protein, 8-12 percent fat, 1.4-1.5 percent n-3HUFA, and 30 mg/kg vitamin C (Giri et al. 1999, Giri et al. 2006, Suwirya et al. 2006). At IMRAD-Gondol and private hatcheries located near IMRAD, fish are fed daily until satiation at 0700, 1000, 1400 and 1600 h. They attain size of 8-10 cm after 6-8 weeks of culture. A total length of 10 cm is the smallest recommended for stocking sea cages for further growth. Health Management Health problems are recognized by private hatcheries as one of the major constraints in grouper hatcheries located in northern Bali. Disease outbreaks are commonly associated with a sudden change in the environment caused by heavy rain or during winter in Australia (July-September) when wind blowing to Bali may cause a drop of seawater temperature from 29 to 24 C. Mass mortalities usually occur in grouper hatcheries with clinical signs such as anorexia and abnormal swimming behavior (swirling) and the causative agents detected in diseased fish were nervous necrosis virus (VNN) and Iridovirus. VNN and Iridovirus are the two most important viruses causing high mortalities in grouper. VNN infection is a devastating disease leading to massive mortalities in grouper larvae and juveniles. Researchers at GRIM have determined that VNN may be transmitted vertically from bloodstock via egg and sperm. Eggs taken from female broodstock by canulation and tested by PCR can be positive for VNN infection. VNN is also transmitted horizontally through water introduced to larval rearing tanks or in live food culture. Our research suggests that most outbreaks of VNN in marine finfish hatcheries in Indonesia are due to horizontal transmission (Koesharyani et al. 1999). Cases of Iridovirus infection in juvenile groupers have been reported elsewhere in Indonesia (Zafran et al. 1999, Koesharyani et al. 2011, Mahardika et al. 2011). Strict biosecurity is the best defense against outbreaks of VNN (Hick et al. 2011). Research and development of recombinant DNA vaccines for VNN and Iridovirus is ongoing. Hatchery Development The established techniques for grouper seed production in Indonesia include hygienic condition of larval rearing water, eggs and live food (Nannochloropsis sp. rotifer and copepod Acartia sp.) and rearing with strict biosecurity practices applied in hatcheries. Strict application of biosecurity in hatcheries are effective to avoid the spread of viral and other diseases. Most hatcheries pay attention to produce good-quality healthy seed free of any kind of diseases. For the industry to move forward, vaccination, early and quick diagnosis of diseases are important and essential for sustainable production (Koesharyani and Novita 2006). More attention to produce specific FIGURE 2. Indoor and outdoor nursery tanks operated by private grouper hatcheries in Gondol, Bali, Indonesia. Note yellow color of tank walls.
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