Effects of Dietary Ascorbic Acid on Tolerance to Intermittent Hypoxic Stress in Japanese Parrot Fish.

Abstract

Control and stressed groups of juvenile Japanese parrot fish Oplegnathus fasciatus were fed diets (moist pellet) supplemented with 0, 75, and 300mg of ascorbic acid (AsA) per 100g. Fish in the stressed group were intermittently exposed to decreasing water oxygen levels every 3 or 4 days for 16 weeks. In the fish given a diet containing no AsA supplement, AsA-deficiency symptoms were manifest-ed earlier, and to a greater extent, in the stressed fish than in the non-stressed ones. Similarly, the growth of stressed fish fed on a diet supplemented with 75mg AsA per 100g was inferior to the growth of the control group, and in the stressed fish there was a reduction in AsA levels in the plasma, kidneys, and gills. On the other hand, fish fed on a diet supplemented with 300mg of AsA per 100g were barely affected by the stressor. These results indicate that, in Japanese parrot fish under these experimental conditions, ex-posure to intermittent hypoxic stress not only induced AsA-deficiency disease early, but also in-creased the AsA requirement. It was also shown that high doses of AsA increased the ability of these fish to resist the stressor.