Some Observations on the Structure and Photomechanical Responses of the Pacific Salmon Retina

Abstract

The general structure of the Pacific salmon retina is described. Rods, single cones and twin cones constitute the visual cell layer which, together with the dense pigment layer, undergoes photomechanical changes common to most teleosts. Stages in the contraction and expansion of rods and cones, and the migration of pigments are depicted.In the laboratory, cultured sockeye salmon became well light-adapted in 20–25 minutes, whereas the time for dark-adaptation was of the order of 55–60 minutes.In the Lakelse River, a sample of natural-run sockeye and coho smolts was found to be fully dark-adapted by about 10:00 P.M. when the light intensity at the water surface was 0.03 foot-candle. Pink and chum fry from Hooknose Creek were similarly dark-adapted by about 9:45 P.M. on an evening when the intensity had fallen below 0.002 ft.-c. At the start of evening migration retinal dark-adaptation in sockeye smolts had just started, whereas in pink and chum fry the retina was approximately half dark-adapted when migration commenced.