Effect of Graded Levels of Supplemental Ascorbic Acid in Practical Diets Fed to Rainbow Trout (Salmo gairdneri)

Abstract

Deficiency symptoms, including anorexia, lethargy, lying prostrate at the bottom of the tank, scoliosis, and lordosis, were noted 20 wk after the start of the experiment in rainbow trout (Salmo gairdneri) held at 15 °C and fed a diet with no supplemental ascorbic acid. The apparent requirement was 40 mg/kg of supplemental ascorbic acid; however, the amount added to trout diets should be in excess of this level due to processing and storage losses and other factors. The ascorbic acid requirement for rainbow trout appears to vary with the age and rate of growth of the trout in that the requirement is higher in young fish. Ascorbic acid was noted to function in the iron metabolism of rainbow trout. Liver and spleen iron levels were correlated with the ascorbic acid level in the diet and suggest either a redistribution of iron stores due to impaired release of iron from reticuloendothelial stores or an increase in the efficiency of intestinal iron absorption. Scorbutic trout developed a gradual but progressive anemia. Key words: ascorbic acid, rainbow trout, vitamin requirement, iron, mineral metabolism, anemia