OSCARS, ASTRONOTUS-OCELLATUS, HAVE A DIETARY REQUIREMENT FOR VITAMIN-C

We found that vitamin C is an essential nutrient for an Amazonian orna mental fish, the oscar (Astronotus ocellatus), This was demonstrated b y the absence of L-gulonolactone oxidase activity, the enzyme responsi ble for the biosynthesis of vitamin C, in liver or kidney of oscars an d by a feeding trial in which oscars without vitamin C dietary supplem entation developed clinical deficiency signs. Fish weighing 29.2 +/- 1 .9 g were divided into four groups, and each group was fed a casein-ba sed semipurified diet containing 0, 25, 75 or 200 mg ascorbic acid equ ivalent (AA)/kg diet for 26 wk. Vitamin C was supplemented in the diet s as L-ascorbyl-2-polyphosphate, a mixture of phosphate esters of asco rbate, which is more stable to oxidation than AA. At the end of 26 wk, fish fed no AA had significantly lower weight gain than fish fed the AA-supplemented diets (P < 0.05). Oscars without dietary AA supplement ation gained only 37% of their initial weight, compared with 112, 102 and 91% gained by fish fed 25, 75 and 200 mg AA/kg diet, respectively. After 25 wk without dietary supplementation of AA, fish began to deve lop clinical deficiency signs, including deformed opercula and jaws, h emorrhage in the eyes and fins, and lordosis. Histology indicated that fish without AA supplementation had deformed gill filament support ca rtilage and atrophied muscle fibers. Collagen content of the vertebral column was significantly lower in fish devoid of dietary AA (P < 0.05 ). Liver AA concentration varied in proportion to dietary concentratio n of AA. The minimum dietary AA concentration tested in this study, 25 mg AA/kg diet, was sufficient to prevent growth reduction and AA defi ciency signs in oscars.