Visual pigments from different parts of the retina in rudd and trout

Abstract

Retinal extracts from the rudd ( Scardinius erythrophthalmus) yield two visual pigments, one based on vitamin A 1 and the other on vitamin A 2. The proportion of the A 1-based pigment was greater in extracts prepared from fish kept under a 20-hr daylength than in those prepared from fish kept under a 4-hr daylength, which confirms previous results. Separate extracts were prepared from the superior and inferior halves of retinas from fish kept under a variety of illumination conditions. In all cases there was a greater proportion of the A 1-based pigment in the superior half, in spite of the fact that this part of the retina normally receives much less light than the inferior half. The effect was not abolished by illuminating the fish from beneath. The same effect was also found in two species of trout ( Salmo fario and rS. gaidneri). Histological preparations of the rudd retina showed that there were more rods in the superior half of the retina, but that the other retinal elements were as numerous above and below the midline. There is therefore more convergence in the superior half of the retina, which may be an adaptation for vision in dim light.