Production of Nutritional Cataract in Trout

Abstract

In 1931 an investigation showed that, in many of the hatcheries of New York State, practically every trout 6 months of age or older had distinct opacities in both lenses (bilateral cataract). The lenses were not the only organs in the fish that were affected. The different fins, including the tail fin, were abnormal and showed signs of alternating periods of partial degeneration followed by partial regeneration. The iris of the eyes in the older fish showed degenerative changes. The scales likewise showed degenerative changes in these older fish. All fish that had well developed cataracts were dark colored, a condition known to occur in fish that are blind.

This investigation was undertaken to determine whether the cataract in these fish was due to a contagious infection or whether such other factors as diet, light and heredity were the cause.

The methods employed here were much the same as those used in previous work (Hess 1 ). Sixteen standard size rearing troughs were used, and were operated at the Caledonia fish hatchery under standard conditions. Fish of 2 different age groups were used, approximately 2 1/2 and 4 months old respectively. There were 2 groups of the younger fish. One (Exps. 4 and 5) were hatched from trout seined from Seneca Lake. The other (Exps. 6, 7, and 8) as well as the older fish used in Exps. 1, 2, and 3 were from hatchery stock. Each trough contained 5000 fish at the beginning of the experiment. Only rainbow trout (Salmo irideus) were used.

To test the possibility of contagion 200 trout with cataract were placed for 4 months in a small pond with 400 trout without cataract and fed the control diet of liver and heart.