[Behavior of trout fry Salmo gairdneri during swinging]

Ten experimental and 10 control experiments on a parallel swing and 4 experiments on a rotating stand were carried out on the fries of the trout Salmo gairdneri, strain Rofor. Depending on changes of motor activity the fish could be divided into three groups: the "freezing" fish, in which the mean swimming rate dropped sharply with the beginning of swinging; (2) the shuttle-swimming fish, in which the mean swimming rate in the process of swinging practically did not change, but which with beginning of swinging started the from-wall-towall swimming in the horizontal plane by changing direction of the movement with a frequency close to the swinging frequency; (3) the "restless" fish, in which significant fluctuations of the meanswimming rate were observed. A decrease of the motor activity in the first group fish seems to be a protective reaction. By freezing, they decrease the vestibular apparatus stimulation. Analysis of the available data allows thinking that the shuttle swimming is based on an unconditional rheoreaction characteristic of pelagic fish. Its realization during swinging depends on activity of otolith organs that until now have not been considered a possible sensor for realization of the rheoreaction. Taking into account the principal role of otoliths in this process, we called this rheoreaction variant the otolithotropic reaction. With increase of stimulus strength, the shuttle movement frequency becomes equal to the stimulation frequency. At the same time, sharpness of the otolith reaction is gradually deteriorated, which, however, is not associated with fatigue of the fish. In fish of the third group, the behavioral changes that are as pronounced as those in fish of the two former groups were not revealed. However, it is to find out the character of behavior of this fish group with increase of time and amplitude of the variable acceleration. Thus, we have managed for the first time to describe a new fish reaction to swinging--the otolith reaction and to confirm the conclusion that the swinging affects the fish motor activity. We suggest that a sharp decrease of the mean swimming rate and a disturbance of otolith reaction are signs of the fish motion sickness.