3-Dehydroretinal (vitamin A2 aldehyde) in crayfish eye

11-Cis-3-dehydroretinal was found in the eye of crayfish, Procambarus clarkii. The 11-cis-3-dehydroretinal was isomerized to all-trans isomer by light-illumination, as was also 11-cis-retinal. Irradiation with deep-red light (lambda greater than 680 nm) selectively isomerized the 11-cis-3-dehydroretinal. The 3-dehydroretinal was not extracted with petroleum ether from the tissue after freeze-drying. These facts suggest that the 11-cis-3-dehydroretinal is the chromophore of crayfish visual pigment. The 3-dehydroretinal content varied with season, high level in winter and low in summer. The crayfish may have a vitamin A1-A2 visual pigment system similar to those of freshwater fishes and amphibians.