EFFECT OF DIET SERIES ON GROWTH, ACTIVITY OF DIGESTIVE ENZYMES AND BODY COMPOSITION OF LARVAL COBIA, RACHYCENTRON CANADUM

Diet is one of the most important conditions during fish early stage especially for marine fishes, and it changes continuously as the fish develops. The experiment was conducted to evaluate the effect of different diets on cobia larvae and acquire the optimal diet combination. The eggs were hatched in a 750L tank in which larvae were stocked for 2 days, then larvae were cultured in a concrete pool on for g days (3-6DAH), feeding on rotifers. On 7DAH, 240 larvae were transferred randomly to twelve 70L tanks with 20 larvae per tank labeled group Ⅰ, group Ⅱ, group Ⅲand group Ⅳ(3 tanks per group). During 7-15DAH, the larvae were fed with rotifers, artemia nauplii, copepods and copepods respectively; during 16-42DAH, with rotifers, artemia nauplii, copepods and fish meal respectively. On 42DAH, all larvae were sampled, weighed and store in -80℃. Crude digestive enzymes were produced from the supernatant by centrifuging homogenized solution of the fish bodies, and the activities of protease, amylase and lipase were analyzed. At the same time, body composition, as well as growth indices of larval cobia were determined. The results showed that： (1) the growth performance of group Ⅳwas the best; (2) the survival of group Ⅲwas the highest; (3) the activities of digestive enzymes and body composition were extremely affected by diet; (4) the protease activity of group Ⅲ, amylase and lipase activity of group Ⅰwas the highest respectively among the 4 groups, and group I was highlighted for its 6.8-11.9 times higher amylase activity than other groups; (5) the crude protein contents of fish bodies were lower than them of corresponding diets, on the contrary, crud fat contents of fish bodies were higher than them of diets. So, there might be compensatory secretion of digestive enzymes, and glucide ＆ fat were utilized preferentially for chronically hungered larvae with fat being more effectively deposited than protein for larval cobia.