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

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 AMP50, 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 AMP205, AMP426 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. (C) 2003 Elsevier Science B.V. All rights reserved.