Effect of ascorbic acid on dietary copper toxicity in rainbow trout ( Salmo gairdneri Richardson)

Abstract

Triplicate groups of juvenile rainbow trout ( Salmo gairdneri) were reared for 16 weeks on practical trout diets containing graded levels of ascorbic acid (0, 100, 1000 or 10 000 mg/kg) with or without a copper supplement of 800 mg/kg. At the end of 16 weeks, trout reared on copper-supplemented diets had significantly lower final body weights than trout reared on diets without supplemental copper. Supplementation with ascorbic acid up to and including 10 000 mg/kg diet did not appear to affect markedly either the absorption or metabolism of copper. However, ascorbic acid supplementation at a level of 10 000 mg/kg did result in a small but statistically significant increase in final body weight of trout reared on 800 mg Cu/kg diet when compared with trout reared on the three lower levels of ascorbic acid. Ascorbic acid concentrations in the head kidney and liver increased with dietary ascorbic acid supplementation, but were not affected by dietary copper supplementation. Copper levels in the kidney, liver and whole body increased with dietary copper supplementation but were not affected by dietary ascorbic acid level. Zinc levels in the liver and whole body increased with dietary copper supplementation while zinc levels of the kidney were not affected. Ascorbic acid supplementation had no effect on the zinc content of the kidney or liver. Iron levels in the kidney were variable, but showed no relation to dietary treatment; however, iron levels in the liver were affected and indicate some interaction in the metabolism of copper and iron in the trout. It was concluded that dietary ascorbic acid supplementation up to 10 000 mg/kg does not significantly alleviate dietary copper toxicosis in juvenile rainbow trout.