According to the importance of vitamin B6 (pyridoxine) as a water-soluble vitamin on the physiological conditions of aquatic animals, the present study aimed to investigate effects of different concentrations of this vitamin in recycle system culture water on the Nile tilapia (Oreochromis niloticus). Treatments including 0 (control), 10, 20, 30, and 40 mg L-1 vitamin B6 were adjusted in triplicate recirculating systems. Each of the experimental tanks (100 L) was stocked 15 fingerling Nile tilapia during 60-day experimental period. According to the findings, weight gain in treatments of 30 and 40 mg L-1 pyridoxine was significantly higher than the other treatments while blood cortisol hormone in the treatment of 40 mg L-1 was significantly highest among the treatments. In addition, mid-intestine trypsin activity in the treatment of 40 mg L-1 was significantly higher than the other treatments. The histological analysis of the intestine showed that the number of mucus-secreting cells significantly decreased in treatments of 30 and 40 mg L-1. Our findings here suggest that pyridoxine can possibly be absorbed by the Nile tilapia's body through culture water and it seems 20-30 mg L-1 pyridoxine in the culture water is the optimal concentration for the Nile tilapia juveniles in recycle system culture.
Keywords: Digestive enzyme; Liver histological changes; Nile tilapia; Vitamin B6 requirement; Water recirculating system.