SCOTOPIC VISUAL PIGMENT COMPOSITION IN THE RETINAS AND VITAMINS-A IN THE PIGMENT-EPITHELIUM OF THE GOLDFISH

Recently, the retinas of goldfish from Grassyfork Fisheries (Martinsville, Indiana 46151, U.S.A.) were reported to possess a rhodopsin with an absorbance maximum at 499 nm, in addition to the known porphyropsin. Rhodopsin and porphyropsin are visual pigments respectively derived from the conjugation of vitamin A1 aldehyde (retinal) and vitamin A2 aldehyde (3-dehydroretinal) to a species-specific opsin. In this study, goldfish from a different supplier (Ozark Fisheries, Stoutland, Missouri 65567, U.S.A.) were also confirmed to possess a rhodopsin with an absorbance maximum at 499 nm. In addition, this paper describes how external factors (photoperiod, light intensity, temperature and exogenous thyroxine) affected the composition of these visual pigments in the goldfish retinas and the vitamins A (retinol/3-dehydroretinol) in their pigment epithelium. After 50 days of acclimation, constant illumination (at 30°C with a 7·5 W incandescent light bulb) and constant darkness (at 30°C) both favored high proportions of porphyropsin (more than 85%) whereas fish held under a 16L/8D cycle (at 30°C with a 7·5 W light bulb) had predominately rhodopsin (less than 10% porphyropsin). Testing at 16L/8D and 30°C, light intensities higher and lower than the equivalent of a 7·5 W bulb (i.e. 6×1013 photons/cm2-sec, 400-750 nm, measured at water surface) both favored significantly higher proportions of porphyropsin. Lower water temperature (10°C and 20°C) or the introduction of thyroxine to the tank water (at a concentration of 100 μg l-thyroxine per liter tank water) also resulted in significantly higher proportions of porphyropsin. Despite the influence of these external factors on the visual pigment composition in the goldfish retinas, the vitamins A (retinol and 3-dehydroretinol) in their pigment epithelium remained predominately 3-dehydroretinol. Although the rhodopsin dominated retinas were always associated with pigment epithelium of slightly lowered 3-dehydroretinol proportions, these results do not agree with previous reports on other species where the proportions of retinol and 3-dehydroretinol mirrored the ratios of rhodopsin to porphyropsin. © 1979.