1. The principal carotenoids of the trout are b-carotene, lutein and astacene. Carotenoids occur in the skin, muscles, ovary, liver and eyes, but the different types are distributed in a characteristic way in the various tissues. Carotene is found in significant amounts only in the liver and ovaries; lutein and astacene together in the skin, muscles and ovaries; lutein alone in the eyes. Xanthophylls, mainly lutein, occur also in the liver. Other carotenoids occur in trace amounts only.
2. The lutein and astacene of skin are in the form of esters. They are located in the xanthophores and erythrophores, of which they are the characteristic pigments. Yellow areas of skin yield mainly lutein, red areas mainly astacene, and their concentration in all parts of the skin is normally several times greater than in any other tissue. In muscle and ovaries both lutein and astacene are present as free hydroxy-carotenoids. Liver contains both free and esterified xanthophylls, the eye tissues only esters.
3. The concentration of the different carotenoid fractions in various tissues was measured with a photoelectric colorimeter in terms of standard preparations of pure carotenoids.
4. Direct measurements of the absorption spectra of xanthophores and erythrophores show that the former contain only lutein, the latter only astacene. Living xanthophores show absorption maxima at 487, about 450 and at 425 mµ; erythrophores a single maximum close to 490 mµ. The maxima in the blue-green are displaced some 10-12 mµ towards the red from their positions in hexane.
5. The concentration of pigment in fully contracted chromatophores was estimated by a visual matching method. Xanthophores were found to contain about 0·00001-0·00003γ of lutein per cell, erythrophores about 0·00020-0·00035γ per cell.
6. Trout kept on a diet low in carotenoids lose most of their red and yellow pigments. Astacene disappears from the skin, and the lutein falls to about one-sixth of the normal level. Feeding with natural foods rich in carotenoids may restore the skin coloration, and fish reared on a natural diet develop normal wild-type pigmentation. Supplements of pure carotenoids added to the basal diet failed to raise the pigment levels of depigmented fish. Trout do not appear to be able to convert one type of carotenoid to another.
- Copyright © 1948 The Company of Biologists Ltd.