Optimal dietary lipid requirement of advanced GIFT Oreochromis niloticus reared at 34 °C water temperature

The objective of this study was to assess the optimal dietary lipid requirement of advanced genetically improved farmed tilapia (GIFT Oreochromis niloticus), reared at 34 °C water temperature. In present study, 360 fish with average initial body weight of (50.88±1.57) g were randomly divided into 6 groups with 3 replicates of 20 fish in each replicate. Fish in each group were hand-fed a purified diets containing different lipid levels 0.22% (control group), 2.83%, 4.98%, 7.45%, 9.23% and 12.47% reared at 34 °C water temperature for 56 days. At the end of feeding trial, growth performance, body composition, serum biochemical indexes and the activities of lipid metabolism enzyme in liver were measured. The results showed as follows: with the increase of lipid levels, weight gain rate (WGR), specific growth rate (SGR), protein efficiency rate (PER) and protein retention rate (PRR) of GIFT O. niloticus were increased at first and then decreased, but feed conversion ratio (FCR) and the feeding intake rate (FIR) presented the opposite trend. The highest hepatosomatic index (HSI) was in 12.47% diet group, the other groups were not significantly different in HSI. During the feeding trial, no fish died. Increasing dietary lipid levels contributed to increased whole body and muscle lipid levels. With dietary lipids levels increased (i.e., from 2.83% to 9.23%), liver crude lipid concentrations were significantly lower than that in the control group. Serum triacylglycerol (TG) and total cholesterol (TCHO) levels tended to increase first then decrease with increasing dietary lipids level. Meanwhile, lipoprotein lipase (LPL) and hepatic lipase activities increased as the level of lipid increased, and were highest in 12.47% diet group; hepatic lipase (HL) activities tended to first increase and then to decrease as the level of dietary lipid increased, and was highest in 2.83% diet group. Regression analysis showed the optimum dietary lipid level for maximum WGR and PER was 4.92% and 5.67%, respectively, and for the lowest FCR was 6.49% when GIFT reared at 34 °C water temperature.