HISTOPHYSIOLOGICAL STUDIES ON THE JUVENILE ATLANTIC SALMON (SALMO SALAR) RETINA: II. RESPONSES TO LIGHT INTENSITIES, WAVELENGTHS, TEMPERATURES, AND CONTINUOUS LIGHT OR DARK

Retinal epithelial pigment dark-adapts in intensities below 10−3 ft-c. Cones are in a light-adapted state in intensities of 10−2 ft-c and above, semiadapted state in 10−3 ft-c, and dark-adapted state in 10−4 ft-c and below. The retinal index corresponds to the response of cones. It is suggested that the visible spectrum of the yearling Atlantic salmon ranges from 3640 Å to 6900 Å because the retina is in a light-adapted state in that range. In light, lower and higher temperatures bring about an expansion of the retinal pigment. Cones and retinal index are not affected. In dark, pigment expands with higher temperatures but temperatures exceeding 18.3 °C bring forth contraction. Cones contract with increasing temperatures but beyond 14.8 °C they expand. The retinal index indicates a greater dark-adaptation of retina with increasing temperatures between 5.0 °C and 18.3 °C but higher temperatures make it less dark-adapted. Cones exhibit no rhythm in their positions in continuous light or dark. Pigment demonstrates no rhythm in light but shows one in dark which persists for a day. The significance of the results is discussed. Comparisons with results with Pacific salmon are made.