Effects of Dietary Lipid Levels on the Growth, Efficiency of Feed Utilizaion and Body Composition of Young Redlip Mullet

Feeding trials were conducted to investigate the effects of dietary lipid levels on the growth and efficiency of feed utilization for young redlip mullet Liza hsematocheila. Experimental diets containing pollack 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 a-starch (35% in experiment I, 44-21.5% in experiment II) as the digestible carbohydrate source were fed to seven groups of experimental fish for eight weeks. In experiment I, the fish fed on 13% lipid and 28% protein diet obtained almost the same growth and feed efficiency as the fish fed on 3% lipid and 48% protein diet. However, according to the increase in dietary lipid level, the lipid contents in dorsal muscle and liver and the liver glycogen content increased, and the protein content in dorsal muscle decreased conversely. Also the visceral ratio to body weight increased significantly with increasing dietary lipid level, therefore the deposition of lipid into fish viscera was indicated on higher lipid diets. When the dietary protein level was constant (experiment II), the best growth and feed efficiency were obtained between 7 and 11% of the dietary lipid levels. On the other hand, better protein 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%