NUTRITIONAL-REQUIREMENTS OF REDLIP MULLET .2. EFFECTS OF DIETARY-LIPID LEVELS ON THE GROWTH, EFFICIENCY OF FEED-UTILIZATION AND BODY-COMPOSITION OF YOUNG REDLIP MULLET

Feeding trials were conducted to investigate the effects of dietary li pid levels on the growth and efficiency of feed utilization for young redlip mullet Liza haematocheila. Experimental diets containing pollac k liver oil (5-15%) as the lipid source, casein (48-28% in experiment I, 40% in experiment II) as the protein source, and dextrin and alpha- starch (35% in experiment I, 44-21.5% in experiment II) as the digesti ble carbohydrate source were fed to seven groups of experimental fish for eight weeks. In experiment I, the fish fed on 13% lipid and 28% pr otein diet obtained almost the same growth and feed efficiency as the fish fed on 3% lipid and 48% protein diet. However, according to the i ncrease in dietary lipid level, the lipid contents in dorsal muscle an d liver and the liver glycogen content increased, and the protein cont ent in dorsal muscle decreased conversely. Also the visceral ratio to body weight increased significantly with increasing dietary lipid leve l, therefore the deposition of lipid into fish viscera was indicated o n higher lipid diets. When the dietary protein level was constant (exp eriment II), the best growth and feed efficiency were obtained between 7 and 11% of the dietary lipid levels. On the other hand, better prot ein and lipid retentions in the body were noted on lower lipid (higher carbohydrate) diets. This indicates that carbohydrate exceeded lipid in the availability as an energy source for young redlip mullet, when the dietary protein level remained around 40%.