1. Introduction
Cobia is an important and popular sport fish in many parts of the world. Its aquaculture has become popular only recently with the success of artificial propagation
and larval production. The cobia is regarded as having the greatest potential among all candidate species for offshore cage culture in Taiwan and other tropical waters. Under
the present cultivating practice, the cobia can attain 4–6 kg in 1 year and survival is
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usually high 90 . About 500 tons of whole fish, averaging 6 kgrfish, were exported from Taiwan to Japan during 1999 at a wholesale price of around US4.8 to 5.7 per kg
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Fish Farming International, January 2000 . The mostly white meat of the fish is served in restaurants as raw fish, sashimi. The belly portion with high lipid content is highly
valued. The cobia is widely distributed in tropical, subtropical and warm temperate seas. A
survey of a natural population in the northeastern Gulf of Mexico revealed that the cobia ranged from age 0 to 9–11 and growth is fast through age 2, after which growth slows
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gradually Franks et al., 1999 . Cobia adults and juveniles mean 340 g were found to Ž
be carnivorous and feed exclusively on small fish, crustaceans and squid Franks et al., .
1996 . They are strong swimmers and aggressive feeders and quite capable of catching mobile prey. They often feed in the water column and possibly near the surface. Under
net cage culture conditions in Taiwan, the cobia are fed either trash fish, or sinking pellets that are modified from feed originally formulated for groupers or seabass. Feed
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conversion ratios FCRs range from 1.6 to1.8. Proximate analysis of a commercial cobia feed revealed a crude protein concentration of 45.3, crude lipid concentration of
16.0 and ash concentration of 11.0. Despite the rapid development of cage culture of cobia and a steady improvement in
feed formulation, little information has been published concerning the nutrient require- ments of this species. Although the preliminary success of commercial compounded
feeds points to a rough estimation of the nutrient requirements of this fish, basic nutritional research is still needed to lay the foundation for further feed development.
The present study investigated the most suitable concentrations of both protein and lipid for optimal growth of juvenile cobia raised in indoor tanks. Proteins and lipids are the
most important chemical ingredients in the diets of most carnivorous fish. The results offer us basic background knowledge on the nutrient requirements of this fish.
2. Materials and methods
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