The effect of supplemental dietary amino acids, minerals and vitamins on salmonids fed cataractogenic diets.

Three nutritional experiments were conducted to determine the effects of various nutrients on the development of ocular lesions in brook trout, Salvelinus fontinalis, lake trout, Salvelinus namaycush, and rainbow trout, Salmo gairdneri. Supplemental methionine prevented development of cataracts and stimulated growth in trout fed diets containing soy protein isolate as the sole protein. Supplemental riboflavin prevented high mortality, cataracts, and other lens-corneal lesions shown in trout fed a semipurified diet containing casein and gelatin. Swim-up fry which were fed a vitamin A-deficient semipurified diet from first feeding grew slowly, developed edema, corneal lesions, and retinal degeneration, but not lens cataracts. In contrast, feeding the same vitamin A-deficient diet to older trout previously fed vitamin A did not cause ocular lesions or other signs of deficiency. Supplemental beta-carotene prevented ocular lesions in swim-up trout held in warm (12.4 degrees C), but not in cold (9 degrees C) water.