The Distribution Of Visual Pigment Within The Retina In Two Teleosts

Abstract

The distribution of the visual pigments within the retina of the rudd, Scardinius erythrophthalmus, and dragonet, Callionymus lyra L., was studied by measuring the spectral absorbance of small areas of intact isolated retinas.The rudd retina contains two visual pigments, VP 5O71 and VP5352. There is a progressive change in the relative proportion of these two pigments in the dorso-ventral plane, and there are no sharply defined zones each with a different pigment mixture. The proportion of the A1-based pigment (VP 5071) is greater in the dorsal part of the retina.The maximal optical density of the pigment in the dorsal retina of the rudd was greater (about o·6) than it was in the ventral retina (about 0·3). The difference in the amount of light absorbed, however, is small compared to the intensity difference between the up-welling and downwelling light of the environment. When the relative proportion of the A1- and A2-based pigments was changed by altering the lighting conditions under which the animals were kept there was little or no change in the maximal optical density of the pigment.In the dragonet the retina shows a clear division into a ventral pink zone (maximal optical density about 0·5) and a dorsal zone that is much paler (maximal optical density about 0·2). The relative spectral absorbance of the two regions is similar, although one is said to be a pure cone region, and the other to be dominated by rods.The spectral absorbance curves for the intact retinas agreed well with results obtained with pigment extracts.