Effects of dietary carbohydrate, lipid and energy on the growth, feed efficiency, and tissue composition of bighead carp (Aristichthys nobilis) fry

Abstract

The utilization of dietary carbohydrate and lipid as energy sources for bighead carp (Aristichthys nobilis) fry and various protein:energy ratios were investigated in a 2x3x3 factorial feeding experiment. Semi-purified diets containing two protein levels (28.9 and 37%) and three levels of lipid (4.26, 5.93 and 6.95%) and carbohydrate (42,48 and 53%) to give different total energy levels were fed to bighead carp fry (48.5 ± 3.5 mg) for 8 weeks.Growth of fry fed diets with 37% protein was significantly higher (P < 0.01) than that of fry fed diets with 28.9% protein level. An increase in dietary lipid from 4.26 to 6.95% depressed growth (P < 0.05). There were no significant differences in feed conversion efficiency (FCE) at varying levels of protein and lipid, although their increments resulted in a decrease in FCE. Increase in dietary protein significantly decreased (P < 0.01) protein efficiency ratio (PER) while increase in dietary carbohydrate significantly decreased (P < 0.05) FCE and PER. Bighead carp fry fed diets containing 3131 and 3470 kcal metabolizable energy/kg and P:E ratio of 92 and 107 mg protein/kcal had the best overall performance. However, the 37% protein diet with approximately 4470 kcal metabolizable energy produced maximum growth. Growth was better with diets containing dietary lipid level of 4.26% and carbohydrate level of 42%. Tissue lipid increased significantly (P < 0.01) with an increase of dietary lipid and carbohydrate. However, inclusion of the highest level of both components in test diets decreased tissue lipid. Tissue protein was significantly higher (P < 0.01) in fry fed high protein diets and low levels of lipid and carbohydrate. Tissue protein, moisture and ash were inversely related to tissue lipid. Survival (%) increased (P < 0.01) with the increase of dietary protein and carbohydrate. Increase of dietary lipid did not significantly affect survival rates of bighead carp fry.