Effects of continuous light on the retina of a fish, Notemigonus crysoleucas

Notemigonus crysoleucas organisms were exposed to light at 1,250 and 850 lux in regimes of 12L:12D and 24L:OD. Each layer of cells in the retina was evaluated employing light microscopy and measurements for quantitative analysis were recorded from the retinas of over 150 fish. These values were compared for dorsal and ventral portions of the retina, for the two intensities, and for the two regimes. Fish maintained under the 24L:OD light regime exhibited significant light damage to the retina, characterized by reduction of outer segments of photoreceptors, reduction in the density of nuclear layers, and disintegration of ganglion cells. The dorsal portion of the retina experienced significantly greater deterioration than the ventral portion. Fish which had been subjected to 96 hours of continuous light displayed no ability to repair damage after 96 hours under 12L:12D.