Pseudo-Rheotropism in Fishes

Abstract

1. Blind goldfish, sticklebacks, eels and Xenopus laevis are insensitive to rectilinear displacements, but respond to all passive curvilinear movements which involve rotation about one of the major axes of the body. In all cases the response is of a dynamic compensatory type in which the animal moves along a curved path, the curvature being in a direction opposite to that of the passive rotation. 2. The ability of blind fish to maintain a fixed position in space when placed in a rotating mass of water is the result of asymmetrical reflex locomotory activity whose rotary and translocatory components tend to be equal and opposite to that induced by the water. This response is almost certainly determined by the semicircular canals of the labyrinth. 3. When a fish is displaced head first by a rotary current of water, marked over-compensatory rotation occurs as soon as the fish comes into contact with a solid surface. A solid surface does not have this effect when the fish is orientated with its head upstream. 4. In the species examined there is no evidence of true "rheotropism".