Abstract
Using the technique of microspectrophotometry (MSP) we have found that the short wavelength sensitive cones in the retina of the pollack (Pollachius pollachius) shift in spectral absorption from a maximum (λ max) at about 420 nm in the violet to about 460 nm in the blue. This shift is not due to chromophore replacement, which substitutes rhodopsin for a porphyropsin, but is more likely to be due to a change in the opsin. The shift appears to be progressive rather than abrupt and coincides with a change in lifestyle of the fish.