Some Quantitative Relations between Visual Stimuli and the Production or Destruction of Melanin in Fishes

Abstract

Fishes (Gillichthys mirabilis) were kept for 3 mos. in glass aquaria, painted black, white and 2 shades of gray. Sets of such aquaria were kept in each of 2 cabinets, lighted by 200-Watt and 10-Watt lamps, respectively. The proportion of melanin in each lot of fishes was then detd. quantitatively by a method specially devised for the purpose. The amt. of melanin varied (1) with the degree of illumination and (2) with the albedo of the background to which the fish were subjected. The mean difference between the lots from the 2 cabinets was not great, being about 7%, in favor of those subjected to the brighter illumination. Much greater differences were shown among the sets kept in the variously painted aquaria in each cabinet. Those from the black aquaria yielded over 30% more melanin than those from the white ones. In the brightly lighted cabinet the amt. of melanin varied very nearly inversely as the logarithm of the albedo of the background.