Effects of different levels of dietary lipids on growth performance, liver histology and cold tolerance of Nile tilapia (Oreochromis niloticus)

This study evaluated the effects of different levels of dietary lipids on the growth performance, feed utilization, body composition and cold tolerance of Nile tilapia (Oreochromis niloticus) fingerlings (7.33 ? 0.12 g fish-1). Four isonitrogenous (275 g kg-1 crude protein), isocaloric (18.5 MJ kg-1) diets containing a mixture of fish oil and corn oil (1:1 ratio) at different levels (70, 85, 110 and 130 g kg- 1) were prepared and fed to Nile tilapia reared at a fixed water temperature 25 ? 1 ?C for two months. After the feeding trial, the fish were exposed to a cold challenge. The best growth rates and feed utilization were achieved at 70 and 85 g kg- 1 dietary lipid, whereas the lowest results were recorded at higher lipid levels (110 and 130 g kg- 1). The ability of Nile tilapia to survive the acute cold stress was significantly improved as the lipid level increased from 70 to 110 g kg- 1 and decreased with further increase in lipid levels. During the cold stress, saturated fatty acids (SFA) significantly decreased, while unsaturated fatty acids (UFA) tended to increase. Thus, this study demonstrates, to a certain level, that high dietary lipid levels have a positive effect on the cold tolerance of Nile tilapia fingerlings.