Effect of Different Levels of Dietary Niacin on the Gut and Liver Histology and Some Liver Enzymes Activity of Juveniles Common Carp (Cyprinus carpio)

This experiment was conducted to examine effects of different levels of niacin on the gut and liver histology and also some activity of the liver enzymes in the blood serum of Common carp. A control diet (containing 30 mg niacin kg-1 commercial diet) and four other diets were prepared which had 50, 70, 90 and 110 mg niacin per kg of commercial diet, added by spraying. Fish with initial average weight of 35 g were allocated to 15 circular 300-L tanks at a density of 12 fish per tank and fed the experimental diets to satiation three times a day for 50 days. The result showed that, the activity of the liver enzymes containing alanine aminotransferase and aspartate aminotransferase decreased with increase of niacin but it was not significantly different (P > 0.05). Also, the increase of niacin induced a significant increase (P