A STUDY OF THE SUCCESSION OF VISUAL PIGMENTS IN PACIFIC SALMON (ONCORHYNCHUS)

Abstract

Retinae of Pacific salmon (Oncorhynchus) have mixtures of two visual pigments, one a retinene₁ (VP 503₁) and the other a retinene₂ pigment (VP 527₂). Retinal extracts were prepared from individuals of five species collected at different times of the year. These extracts were subjected to partial bleaching experiments to determine the proportions of the two visual pigments. Liver extracts were prepared and the percentages of vitamin A₁ and vitamin A₂ were estimated in these extracts by means of the Carr-Price (antimony trichloride) colorimetric reaction. There was a progressive increase in the percentage of VP 527₂ in retinae of adult coho, king, pink, chum, and sockeye salmon during the spawning migration. Except for the sockeye salmon, this increase resulted in a conversion from a retina having predominantly VP 503₁ to one having a preponderance of VP 527₂- Juvenile coho and king salmon exhibited changes in the proportions of the two visual pigments during the year, but similar changes did not occur in juvenile sockeye salmon. The percentage of VP 527₂ in the retina is not a simple function of the proportion of vitamin A₂ in the liver; however, there was an increase in the percentage of vitamin A₂ in the liver of adult salmon which accompanied the increase in the proportion of VP 527₂.