Rod and cone visual pigments in the goldfish.

This microspectrophotometric (MSP) study has confirmed that goldfish, acclimated under a certain light and temperature regimen, possess mixtures of porphyropsin and rhodopsin in their rod outer segments. Moreover, the MSP spectra from the red, green and blue cones of these acclimated goldfish also shifted to shorter wavelengths from spectra of pure 3-dehydroretinal based visual pigments. Thus, goldfish retinas may possess a total of eight visual pigments (two rod pigments and six cone pigments) instead of four (one rod pigment and three cone pigments). Possibly, a common control mechanism, governed by external conditions, regulates the utilization of retinal and 3-dehydroretinal for the biosynthesis and/or regeneration of visual pigments in both rods and cones. Tsin and Beatty (1978) have recently reported the presence of a rhodopsin, P499i, (a visual pigment based on retinal) in addition to the previously known porphyropsin, P5221, (a visual pigment based on 3-dehydroretinal) in digitonin extracts of the retinas of goldfish, Carassius auratus. In a subsequent study, it was found that the rhodopsin to porphyropsin ratio could be changed from about 1: 9 to 9: 1 by an acclimation regimen involving temperature, light intensity and photoperiod (Tsin and Beatty, 1979). In the above studies, however, it was not possible to determine whether the cones may also have been induced to change from 3-dehydroretinal to retinal based visual pigments by the acclimation regimen. The rudd, Scardinius erythrophthalmus, is a fish known from analyses of retinal extracts to possess both a rhodopsin, P510,, and a porphyropsin, P5402 (Dartnall et al., 1961). A recent MSP study of this fish (Loew and Dart&l, 1976) found PSlOr and P54Ot mixed in rods with individual rods having A,,, values between 517 and 540 nm. Each of the three spectral types of cones were also found to contain mixtures of retinal and 3-dehydroretinal based visual pigments with A,,,,, values for red cones between 570 and 625 nm; for green cones between 507 and 523 nm; and for blue cones between 450 and 460 nm. The authors concluded that the red cones have the pigment pair P562r and P62Ot, and the green cones have the pair P5OOt and P523*. An estimate of the A,,,,, value for each of the two pigments in the blue cones, however, was not given. For the red and green cones, the pigment pairs were in a ratio that was, in each case, similar to that for P51Or and P5402 in nearby rods. Moreover, rudd that were rich in the 3-dehydroretinal based rod pigment (P540,) when maintained in a 12L/12D condition, had increased retinal to 3-dehydroretinal based pigment ratios in both rods and cones when transferred to continuous light, .a condition known to favor increased retinal based rod pigment (P51Ot) in extracted retinas (Dartnall et al., 1961). The microspectrophotometric (MSP) measurements on goldfish cones by Liebman and Entine (1964) and Marks (1965) were among the first successful attempts to determine the spectra of cone pigments in individual cells. Although the J.,,,,., values reported by these authors differed slightly for the individual goldfish cone pigments, they were assignable to three &,,,., regions; near 455 nm for blue cones, 535 nm for green cones, and 625nm for red cones (Leibman and Entine, 1964; Marks, 1965; Harosi and Mac&hoi, 1974; Stell and Harosi 1976). In none of these studies was there any suggestion of more than one visual pigment in each spectral type of cone and Harosi and MacNichol (1974) concluded that the experimental’ evidence supported 3-dehydroretinal as the prosthetic group for each of the three goldfish cone pigments. The purpose of the present preliminary investigation was to use MSP to determine whether goldfish, which had been held in a photic and thermal environment that favored high proportions of rhodopsin, P499t, would also have a retinal based cone pigment paired with each of the 3-dehydroretinal based cone pigments. Such goldfish would than have six cone pigments instead of three and eight visual pigments in all. One year old comet goldfish were obtained from Grassyfork Fisheries (Martinsville, IN 46151, U.S.A.) in April, 1978 and held at 30°C under fluorescent light on a natural photoperiod in the laboratory at the University of Alberta. They were fed daily with Ewos fine pellets. On February 26, 1979, 30 of these fish were transferred to a covered tank and conditioned to a temperature (30°C) and a light regime (16L/8D from a 7.5 W Tungsten bulb) known to favor a high proportion of rhodopsin in retinal extracts (Tsin and