Locomotor activity of atlantic salmon parr ( Salmo salar L.) in various light conditions and in weak magnetic fields

Abstract

Locomotor activity studies in the laboratory under artificial light cycles co-ordinated with times of sunrise and sunset demonstrated that ten of sixteen Atlantic salmon parr were nocturnal, with an approximately twenty-four hour periodicity. The remaining six fish exhibited diurnal activity patterns or activity mainly after times of light change. Two fish immediately shifted their activity patterns to co-ordinate with a 6-hr shifted light cycle. Six fish retained no activity patterns in constant light, and only two of eleven fish had weak activity patterns in constant darkness. Results suggest that Atlantic salmon parr are dependent on a light-dark cycle for timing their activity rhythms. Three of twelve salmon in an imposed magnetic field four times the strength of the horizontal vector of the ambient field, increased their activity level and changed activity patterns in the increased field. The remaining fish showed no distinct change in locomotor activity.