Effects of Low Dietary Fishmeal on Growth, Nitrogen Loading and Some Physical and Chemical Indices of Asian Sea Bass Lates calcarifer (Bloch, 1790)
A 60-day trial was conducted to determine the effects of a low-fishmeal diet on Asian sea bass, Lates calcarifer. A 50% fishmeal diet was used as a control and in other experimental diets, fishmeal was replaced by soybean and canola meals to give diets containing 40, 30, 20 and 10% fishmeal. The effect of supplementing the 10% fishmeal diet with 1% betaine was also tested. Fish fed the 10–30% fishmeal diets showed significantly higher specific growth rate than did fish fed the control diet. Reducing the amount of dietary fishmeal did not affect the fish survival rate, feed intake or feed conversion ratio, but decreased the nitrogen loading. Reduced dietary fishmeal increased the amount of flesh protein and most essential amino acids contents, but decreased the flesh lipid, ash and bone protein contents. The hepato-somatic and viscero-somatic indices and the condition factor were significantly increased with reducing dietary fishmeal. Supplementing the 10% fishmeal diet with 1% betaine reduced the hepatosomatic index and condition factor, but increased the feed intake, feed conversion ratio and nitrogen loading; however, this did not improve the specific growth rate and survival rate, and adversely affected fish quality by decreasing the flesh protein and increasing the lipid content.