Evaluation of dietary Vitamin C requirement of Hypophthalmichthys molitrix fingerlings and its effects on growth, haematology and serum enzyme activities

Abstract

Vitamin C (VC) is a necessary nutrient for normal fish physiology and immunity. Therefore, A 60-day feeding trial was designed to evaluate the dietary VC requirements of silver carp (Hypophthalmichthys molitrix). Six isocaloric and isonitrogenous diets were formulated by incorporation of VC at 0, 50, 100, 200, 400 and 800 mg kg−1 levels and the analysed VC content in diet was 5.7, 51.1, 95.3, 191.6, 370.7 and 757.5 mg kg−1 respectively. At the trial termination, VC supplementation significantly enhanced the growth and feed utilization. The highest values for whole body crude protein were recorded at 95.3 and 191.6 mg kg−1 of VC. In comparison to the basal diet, VC supplementation improved (p < 0.05) the whole body crude fat. Dietary VC had a dose-dependent effect on the white blood cell count and haematocrit. A significant increase in the alkaline phosphatase activity was recorded for fish fed 5.7 to 95.3 mg kg−1 of VC, attaining a constant value afterwards (95.3–757.5 mg kg−1 of VC). In comparison, dietary VC decreased (p < 0.05) the aspartate aminotransferase and alanine aminotransferase activities. Similarly, the glucose content also decreased significantly from 5.7 to 95.3 mg kg−1 of VC and became constant thereafter. Dietary VC supplementation significantly affected the antioxidant enzyme activities. The liver VC content showed a dose-dependent relation, where the VC content increased with the increase in VC supplementation reaching the highest value at 757.5 mg kg−1. Moreover, VC-fed fish showed an increased (p < 0.05) survival against Aeromonas hydrophila challenge. On the basis of broken-line regression, the optimum dietary VC requirement of H. molitrix for weight gain% and liver VC content is 61.31 and 241.13 mg kg−1 respectively.