Dietary vitamin C requirement of genetically improved farmed Tilapia, Oreochromis Niloticus

A 12‐week growth experiment was conducted to quantify the appropriate dietary vitamin C requirement for GIFT tilapia Oreochromis niloticus . Triplicate groups of 25 experimental tilapia [initial body weight: (70.0 ± 1.6) g] were cultured in 5.6‐m 3 aquaria ( r  =   1.5 m, h  =   0.8 m) and fed with semi‐purified diets containing six levels [6.1 (un‐supplemented diet], 23.8, 41.9, 85.1, 167.4 and 339.0 mg kg −1 diet respectively) of vitamin C (supplied as L‐ascorbyl‐2‐polyphosphate). The results showed that, increasing dietary vitamin C level up to 41.9 mg kg −1 diet increased weight gain rate of tilapia, beyond which it remained nearly unchanged. Vitamin C contents in liver and muscle presented first increased linearly then tended to reach saturation at high vitamin C (167.4 and 339.0 mg kg −1 ) treatments. Muscle collagen content significantly increased with increasing dietary vitamin C levels. Whole‐body lipid content significantly increased, whereas ash content significantly declined, but moisture and crude protein content showed no significant difference with the increasing of dietary vitamin C. The blood chemistry analysis showed that dietary vitamin C had significant effects on enzyme activities of serum alkaline phosphatase, aspartate aminotransferase and alanine aminotransferase. Significant effects were also observed on albumin and total protein content of serum, but haemoglobin content showed no significant differences among all the treatments. The vitamin C requirement for GIFT tilapia was estimated to be 45.0 mg kg −1 diet based on maximum growth, 114.9 and 118.6 mg kg −1 diet based on maximum liver and muscle vitamin C concentration respectively.