Duplicate groups of small coho salmon and rainbow trout were fed a water‐soluble vitamin test diet containing 0, 5, 10, 20, 40 or 100 mg of ascorbic acid per 100 g of dry diet. Both salmon and trout fed deficient diets developed acute lordosis or scoliosis with resultant high mortality. Rainbow trout appeared to exhaust ascorbic acid reserves more rapidly than coho salmon. Blood levels of ascorbate reflected diet content of vitamin C at lower levels of intake and anterior kidney tissue content increased directly with C level in diet. Wound repair was delayed or inhibited in fish on low C diets and results generally supported diet and tissue levels needed for rapid growth and absence of histopathology. A dietary need for vitamin C for both species was evident.