Carotenoid Pigmentation of Trout

Abstract

Trout kept in aquaria and fed on a diet of chopped meat and earthworms lose the brilliant yellow and red pigmentation characteristic of wild fish, but do not appear to suffer any other inconvenience. The xanthophore and erythrophore cells of the dermis become few in number and those remaining contain little pigment. As reported in a separate communication1, the pigments specifically concerned in these changes are esters of the carotenoids lutein and astaxanthin. The melanophores are not affected. I find that the total carotenoid content of the skin and fins of depigmented fish is about a tenth that of the wild type (see accompanying table). Moreover, all the pigment remaining in the former is lutein, whereas in the latter lutein and astaxanthin (estimated as astacene) are present in much the same concentration. Trout reared from eggs in this laboratory in a balanced tank and fed solely on ‘natural’ foods consisting of such organisms as they could capture, supplemented from time to time by quantities of live Entomostraca, chiefly Simocephalus and Daphnia species, and larvae of Corethra, have developed the typical pigmentation of wild fish. They have bright red spots on both sides of the body, the tip of the adipose fin and the dorsal and ventral edges of the tail are also red, the pectoral and pelvic fins are bright orange and the skin of the belly golden. The concentration of carotenoids and the ratio of lutein to astacene are of the same order as found for wild trout.