Vitamin B6 requirements of tilapia Oreochromis niloticus x O-aureus fed two dietary protein concentrations

A feeding trial was conducted to determine the adequate level of dietary vitamin B-6 (pyridoxine, PN) for juvenile tilapia Oreochromis niloticus x O. aureus fed diets containing different dietary protein concentrations. Purified diets with eight levels of PN (0, 2, 4, 8, 12, 20, 50, 100 mg/kg diet) at either 28 or 36% protein concentration were each fed to three replicate groups of tilapia (mean weight: 0.73 +/- 0.01 g) for 8 weeks. Results indicated that in the 28% protein group, fish fed 4 mg PN/kg diet had a more significant (p<0.05) weight gain than fish fed 0 and 100 mg PN/kg diet; feed efficiency ratio (FER) of fish fed 4 mg PN/kg diet was higher than fish fed 0 and 8-100 mg PN/kg diets. In the 36% protein group, fish fed 12-50 mg PN/kg diets had higher weight gain than fish fed 0, 100 mg PN/kg diets and fish fed 20 mg PN/kg diet had higher FER than fish fed 0-4 mg PN/kg diets. Hepatic alanine aminotransferase (ALT) activity generally increased with increasing dietary vitamin B-6 and leveled off at 12 mg PN/kg and 20 mg PN/kg in the 28% protein and 36% protein groups, respectively. Tilapia fed 100 mg PN/kg diet at 28% protein concentration showed normocytic normochromic anemia symptoms. Weight gain and ALT activity analyzed by broken-line regression indicated that the optimum dietary vitamin B-6 requirement in juvenile tilapia were 1.7-9.5 mg PN/kg and 15.0-16.5 mg PN/kg diet in 28% and 36% protein diets, respectively.