Effects of dietary lipid levels on growth,muscle composition and digestive enzyme activities of juvenile GIFT strain Nile tilapia,Oreochromis niloticus

Abstract:

The objective of this study was to determine the effects of dietary lipid levels on the survival,muscle composition and digestive enzyme activities of juvenile GIFT strain Nile tilapia,Oreochromis niloticus. Triplicate groups of fish were fed for 90 days with the experimental diets formulated with increasing lipid levels (1.73%,3.71%,5.69%,7.67%,9.64% and 16.55% lipid) using fish oil (0%,2%,4%,6%,8% and 15% fish oil respectively ) as the lipid source. Survival rate throughout the growth trial ranged from 84.76 to 99.05%,but the survival rate of fish fed the 16.55% lipid was signifcantly less than the 3.71% lipid diets (P<0.05) . Daily feed intake (I_DF) was variable (0.94±0.04) to (1.34±0.02) g/d and signifcantly declined by dietary treatments when the lipid level higher than 7.67% (P<0.05) . Final mean body weight,and final mean body length were signifcantly greater for diets 7.67 L compared to the 1.73% and 16.55% treatments (P<0.05). Lipid content of muscle increased with increasing dietary lipid levels by the range of 2.29% to 4.27%,protein,ash and phosphorus contents had a rising trend. The protease activities of stomach and intestine had not signifcantly changed between treatments (P>0.05) ,but the lipase activities of foregut and midgut and amylase activities of foregut were significantly declined with increasing dietary lipid levels (P<0.05) . The results showed that high lipid level diets could cause the fish survival rate and daily feed intake to go down. With increasing dietary lipid levels for the tilapia,lipid content of muscle rose,protease activities of stomach and intestine changed a little,but lipase activity of intestine was restrained.