The photosensitive retinal pigments of fishes from relatively turbid coastal waters.

Digitonin extracts have been prepared from the retinae of a dozen species of marine and euryhaline teleost fishes from turbid water habitats. Spectrophotometric analysis of the extracts shows that the photosensitive retinal pigments of these species have maximum absorption above 500 mmicro. In nine species there are retinene(1) pigments with lambda(max) between 504 and 512 mmicro. In the marine but euryhaline mullet, Mugil cephalus, there is a porphyropsin with lambda(max) 520 mmicro. A mixture of rhodopsin and porphyropsin in an extract of a marine puffer, Sphoeroides annulatus, was disclosed by partial bleaching with colored light. In addition, one other species has a 508 mmicro pigment, of which the nature of the chromophore was not determined. The habitats in which these fishes live are relatively turbid, with the water greenish or yellowish in color. The spectral transmission of such waters is probably maximal between 520 and 570 mmicro. It is suggested that the fishes have become adapted to these conditions by small but significant shifts in spectral absorption of their retinal pigments. These pigments are decidedly more effective than rhodopsin in absorption of wavelengths above 500 mmicro. This offers a possible interpretation of the confusing array of retinal pigments described from marine and euryhaline fishes.