Vision and Guanine Production in Fishes

Abstract

Guanine detns. were made on the skin of immature specimens of the marine fish Girella nigricans which had been kept 4 mos. in bowls painted black, white and 3 intermediate shades of gray. An extract of the dried skin with H2SO4 was made slightly alkaline with NaOH and tested for purines by Cu bisulfite precipitation and a colorimetric estimation with phenol reagent. The guanine/g. body wt. (or/g. of dry skin weight) decreases with darker environment. Taking white as 100 the albedo of pale gray is 37.74 and from there down to black (1.42) the quantity of guanine decreases at a greater rate. As melanin values from black to pale gray vary inversely as the log. of the albedo, 2 important metabolites, melanin and guanine, are strongly influenced by the visual field of the fish in such a way as to make for the animals'' concealment.