INFLUENCE OF LIGHT INTENSITY ON RETINAL ADAPTATION IN ATLANTIC SALMON (SALMO SALAR) YEARLINGS

Abstract

Retinae of fish exposed to 9 × 10² ft-c are more fully adapted to light than those of fish exposed to 10⁻¹ ft-c. Retinae of the former group take a shorter time to attain the same state of adaptation as that of the latter. However, they take a longer time than the latter to attain their own maximum state of adaptation. Retinae of fish subjected to darkness after exposure to 9 × 10² ft-c are not dark-adapted even after 70 minutes. The retinal epithelial pigment of fishes placed in darkness from light of 10⁻¹ ft-c dark-adapts in 45 minutes while the cones do so in 25 minutes. The retinal index indicates that dark-adaptation occurs 45 minutes after subjection to dark. Hypotheses presented in a previous paper are discussed in the light of these results.