Phototropism in fishes,and its relation to the results obtained by eye-dislocation

Summary In the case of viviparous perch and goldfish, unilateral blinding causes a tilting on the anterior-posterior axis towards the normal eye, the amount of tilting being dependent upon the intensity of light. With a sudden change to a greater intensity of light, the fish circle toward the blind eye, and upon sudden reduction of the intensity they often circle toward the normal eye. The similarity of this reaction to the effect of unilateral blinding of insects is offered as an explanation.It is suggested that these results explain the experiments of Pearcy and Koppanyi. These workers dislocated one eye of a goldfish and removed the other one, explaining the consequent tilting of the fish as due to an attempt of the animal to regain its normal visual field. Since the fish was now totally blind, due to the effect of the operation, no tilting was present. As the dislocated eye. gradually recovered its vision, the fish began to tilt, reaching maximal tilting several weeks afterwards. However, since I have produced tilting by unilateral blinding alone, it seems evident that the results obtained by those two experimenters were also due to unilateral blinding, and not to dislocation of the eye.I am indebted to Dr. A. R. Moore both for the suggestion of the problem and for advice during the experiments.