Xanthophylls, and less frequently carotenes, have been identified in the skin of many species of fish, and are the usual pigments of the xanthophore cells1. The properties of these carotenoids, however, do not recommend them as the pigments of the red erythrophores, which are a prominent feature of the colour pattern of many Salmonidae. Astacene was extracted from the skin of the goldfish and other species by Lederer2, and would seem a more probable substance for the erythrophores. I have made repeated analyses of portions of the skin and fins of wild trout, Salmo trutta, which have yielded two types of carotenoid, both of them present in the tissues as esters. One exhibits after saponification the properties of a dihydroxy-carotenoid or xanthophyll, with absorption maxima about 475 mµ and 447 mµ in hexane, and at about 512 mµ, 475 mµ and 450 mµ in carbon disulphide. It is indistinguishable on a mixed chromatograph from a standard solution of lutein, but probably consists of a mixture of lutein with a small proportion of its isomer zeaxanthin. The other carotenoid possesses acidic properties. It remains in the alcoholic saponification residue after the xanthophyll fraction has been removed, and is itself extracted therefrom by petroleum after acidification. Crude extracts show a single broad maximum about 475 mµ in hexane and about 490–495 mµ in pyridine; but after purification by adsorption on columns of magnesium oxide or alumina two or three times, the absorption maximum in pyridine is at 499 mµ. Small amounts of deep purple crystals were obtained, which were insoluble in hexane, slightly soluble in methyl alcohol but dissolved easily in pyridine. These properties serve to identify the pigment as astacene, and since this substance is now generally regarded as a reaction product of astaxanthin, the skin pigment is presumably an ester of the latter.