Rhythmicity of chromophore turnover of visual pigment in the Antarctic amphipod Orchomene plebs (Crustacea; Amphipoda)

1. Relative retinal amounts in the compound eye of the Antarctic amphipod Orchomene plebs were assessed during conditions of continuous summer daylight every 3 h over a period of 48 h. The habitat of the experimental animal is the bottom of the Ross Sea (78°S; 166°E) down to depths of at least 400 m; water temperature is a constant — 1.8° C. A periodicity of 12 h was detected with relative amounts of 11-cis retinal exhibiting peaks at midday and at midnight and troughs at 7.00 h and 19.00 h.
2. The result that 90% of retinoid were insoluble in n-hexane suggests that at least 90% of the measured retinoid were attached to membrane-bound proteins such as opsin.
3. Selective light adaptation showed that the visual pigments were thermostable and photoregenerable. The main absorbance peak of rhodopsin, compared with metarhodopsin, seems to be in the longer wavelengths.