Effects of the different levels of dietary vitamin C on growth and tissue ascorbic acid changes in parrot fish ( Oplegnathus fasciatus)

Abstract

An 11-week feeding trial was conducted to study the effects of the different levels of dietary vitamin C on growth, tissue ascorbic acid concentrations and histopathological changes in parrot fish. Casein and gelatin-based diets were formulated to contain 0, 60, 120, 240, 480 and 2000 mg l-ascorbic acid (AA) per kg diets on AA equivalent basis in the form of l-ascorbyl-2-monophosphate (AMP), 60 and 240 mg AA per kg diet as l-ascorbic acid. However, the analyzed AA levels were 0, 50, 100, 205, 426 and 1869 mg AA per kg diet in AMP supplemented diets; 36 and 149 mg AA per kg diet in l-ascorbic acid supplemented diets. Thus, the diets were designated as AA-free, AMP 50, AMP 100, AMP 205, AMP 426, AMP 1869, AA 36 and AA 149. Fish averaging 3.9±0.06 g (mean±S.D.) randomly were fed the experimental diets in triplicate groups for 11 weeks. Weight gain (WG) of fish fed AMP 50 and AA 36 diets were significantly lower than those of the other groups, and fish fed AMP 1869 diet showed a higher WG than did fish fed AMP 50, AMP 100, AMP 205, AA 36 and AA 149 diets ( P<0.05). However, there was no significant difference in WG between fish fed diets AMP 426 and AMP 1869, and among fish fed AMP 100, AMP 205, AMP 426 and AA 149 diets. Fish fed the AA-free diet began to show deficiency signs, such as retarded growth, darkening, anorexia and high mortality, after 3 weeks of feeding trial. After 6 weeks of the feeding trial, liver from fish fed the AA-free diet showed severe atrophy. By the end of the seventh week, all fish fed the AA-free diet were dead. Liver AA concentration from fish fed AMP 50 diet was significantly lower than that from fish fed AMP 205, AMP 426, AMP 1869 and AA 149 diets, and fish fed AMP 50, AMP 100, AA 36 diets showed a significant lower AA concentration in liver than did fish fed AMP 205, AMP 426 and AMP 1869 diets. Broken line analysis of weight gain indicated that the dietary vitamin C requirement of parrot fish is 118±12 mg AA per kg diet in the form of l-ascorbyl-2-monophosphate for maximum growth.