Growth performance of common carp, Cyprinus carpio fed varying lipid levels through low protein diet, with a note on carcass composition and digestive enzyme activity

Protein sparing by lipid has been demonstrated in certain cultivable species of fish. This study was carried out using four low protein isonitrogenous diets (24% crude protein) formulated by supplementing varied levels of fish oil (0, 3, 6, and 9%). The diets were fed for 120 days at 5% body weight to triplicate groups of common carp (av. wt. 2.13-2.21 g) stocked at 1 per m2 in mud bottomed cement tanks (18 m2), fertilized with poultry manure. The growth of fish was the highest (P < 0.05) with the diet containing 6% fish oil, followed by 3, 9, and 0%. Food conversion ratio and protein efficiency ratio improved with increasing dietary lipid level. Dietary lipid had a positive impact on carcass lipid level (P < 0.05). Moisture and crude protein did not vary (P > 0.05) from that of the control. Survival ranged from 96.29 (T1) to 100% (T0) without any significant (P > 0.05) difference among the treatments. While there was a general increase in amylase activity in the treated fish, protease activity showed a reduction with increase in oil supplementation. No difference (P > 0.05) in lipase activity was observed between the different treatments. The results indicate the beneficial effects of incorporating fish oil in the diet of common carp.