The Dietary Niacin Requirement of Large GIFT Tilapia

Total 360 large GIFT tilapia, Oreochromis niloticus, with average initial body mass of (220.16±7.66) g were randomly divided into 6 groups consisting of 3 replicates (20 fish per net). Each group was fed a diet that mass fractions of niacin were 11.84 (control group), 37.78, 64.70, 89.44, 157.15, 335.36 mg·kg^-1 for 10 weeks. Growth, feed utilization, body composition, some serum biochemical indices and liver niacin concentration were measured to detect the suitable requirement of niacin in diet of large GIFT tilapia. The results showed that the addition of niacin to diets significantly improved fish mass gain rate(MGR, %) and feed efficiency(FE); the crude protein content in whole-body of fish in the 157.15 and 335.36 mg·kg^-1 groups was significantly higher than that of other groups. The crude lipid content of fish in the 64.70 mg·kg^-1 group was the highest and significantly higher than that of the control group; there were no significant differences in carcase moisture and crude ash of the fish. The serum total cholesterol(T-CHO, mmol·L^-1), high density lipoprotein cholesterol(HDL-C, mmol·L^-1) and total protein(TP, mmol·L^-1) content first increased then decreased as the level of dietary niacin increased, and they reached the peak when feeding the fish mass fraction of niacin 157.15 mg·kg^-1. The addition of niacin to diets significantly reduced serum triglyceride(TG, mmol·L^-1) content. The niacin content in liver first increased then plateaued with increasing dietary niacin levels and it was significantly higher in the niacin added groups than that of the control group. Regression analysis showed that large GIFT tilapia were estimated to need mass fraction of niacin 63.62, 158.52-172.41 mg·kg^-1 respectively to maintain their maximum growth and normal physiological function.