Retinomotor Cycles and Correlated Behavior in the Teleost Astyanax mexicanus (Fillipi)

Dark-adapted Astyanax exposed to light at 5 ft-c schooled in about 15 sec during the day, but only after a lapse of about 6 min at night. This behavioral rhythm was closely synchronized with the natural diel cycle and was correlated with a retinomotor rhythm. At night the retina was histologically dark-adapted. During the day it was in an intermediate condition with the rods and cones, on the average, near their light-adapted positions. The pigment was in part concentrated near the basal cell layer as in the dark-adapted retina. The remainder was extended as in the light-adapted retina but did not form a dense light-occluding band proximal to the rod ellipsoids.