In 1957, when control of the sea lamprey appeared imminent, production of lake trout (Salvelinus namaycush) in hatcheries was increased. Coincident with this increase, certain diseases of lake trout became evident. One disease, cataract, results in permanent damage to the eye Several experiments to investigate the cause of cataract were conducted over a period of 3 years; 3 with diets, 3 involving light intensity (Allison, 1962), 1 in handling, and 1 experiment with injections of excess riboflavin. The experiments with diet, handling, and riboflavin injections did not provide control of cataract.