Hypervitaminosis A in rainbow trout (Salmo gairdneri): toxicity signs and maximum tolerable level

Duplicate groups of juvenile trout were reared on practical trout diets supplemented with geometrically increasing levels of vitamin A (as retinyl palmitate) from 4,000 to approximately 8,104,000 IU/kg diet for 16 weeks at 15.2 +/- 0.5 degrees. The major signs of hypervitaminosis A in rainbow trout were growth depression, increased mortalities, abnormal and necrotic anal, caudal, pectoral and pelvic fins, and pale-yellow, fragile livers. The maximum tolerable level of vitamin A in rainbow trout is approximately 904,000 IU/kg diet, whereas levels above 2,704,000 IU/kg diet are toxic. Hypervitaminosis A in trout also resulted in the occurrence of some spinal deformities; however, there was no apparent effect of excess vitamin A on ascorbic acid metabolism. Liver iron levels declined with increasing levels of dietary and liver vitamin A, indicating an effect of vitamin A on liver iron metabolism in trout. No effect of increasing dietary vitamin A was apparent in the mineral content of the kidney, skin-scales and vertebrae.