SPECTRAL CHARACTERISTICS OF VISUAL PIGMENTS IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

We investigated retina preparations of young rainbow trout (Oncorhynch us mykiss) with body wt 5-40 g. Rods, single and double cones were mea sured in side-on orientation by microspectrophotometry, identifying fi ve spectrally distinct visual pigments (or photoreceptors containing m ixtures of visual pigments). The mean wavelength of peak absorbance (l ambda(max)) of the alpha-bands were 365 and 434 nm in single cones, 53 1 and 576 nm in double cones, and 521 nm in the rods. The half-band wi dth (HBW) of the main absorption bands were broader than expected of r etinal- (vitamin A(1)-) based visual pigments, and thus, they were ind icative of a mixed chromophore pool derived from both the vitamin A(1) and A(2) forms. One consequence of the utilization of mixed chromopho res is the broadening of the alpha-band absorption in each pigment typ e. And yet, we obtained exceptionally narrow HBW for the UV-type pigme nt, when compared with HBW values expected on the basis of the linear trend seen in visual pigments absorbing in the visible spectrum, We co nclude that the UV pigment in rainbow trout has an unusually narrow HB W. Nevertheless, this species is not exceptional in this regard, for t he UV-absorbing visual pigments in other vertebrate species also have narrow HBW.