THE STRUCTURE AND FUNCTION OF THE GUT IN SURF PERCHES (EMBIOTOCIDÆ) WITH REFERENCE TO THEIR CAROTENOID METABOLISM

Abstract

1. A yellow, orange, or red pigmentation of the rectal segment of the intestine in certain surf perches is described and illustrated. 2. The carotenoid pigments of the shrimps consumed by the perch Cymatogaster aggregatus, the xanthophyll of the fishes' intestines and recta, and the xanthophyll ester, mainly of the skin, are described with respect to chemical and spectroscopic properties. 3. Carotene (apparently mainly the α-isomer), a red acidic carotenoid (not astacene), and a xanthophyll (or a mixture of two xanthophylls which were not separated) similar in chemical and spectral absorption properties to taraxanthin, are found in the shrimps (mainly Hippolyte californiensis). The acidic carotenoid and the xanthophyll(s) are present as epiphasic esters. 4. Both the red acid and xanthophyll are hydrolyzed and rendered hypophasic in the alimentary tract of Cymatogaster, but the xanthophll(s) are apparently the only carotenoids absorbed by the intestine. 5. The carotenoid pigments of the rectal mucosa consist of the same xanthophylls as those in the shrimps, but unlike the latter, are stored in this tissue in unesterified condition. When the fish are not given food containing a supply of the carotenoid, the pigmentation of the rectal segment fades rather soon and may disappear completely in a few days. 6. The xanthophyll stored in the skin and perhaps in certain other tissues of the perch is re-esterified, and appears to be a single xanthophyll. It is small in quantity (0.26 to 0.27 mg. per 100 grams of wet, eviscerated fish tissue) and constant, whether the fish are gorged with shrimps or starved for some days or weeks in the laboratory. 7. Observations and experiments lead the authors to offer the following provisional conclusions regarding the metabolism of the xanthophylls of rectal tissue: a. The carotenoid material is not absorbed directly from the lumen of the rectum by the rectal mucosa, but is taken up by the mucosa of the intestine proper, and carried by the blood to the rectal tissue; when present in the blood in concentrations which exceed some threshold value, the xanthophyll pigment accumulates in the rectal mucosa; b. The rectum does not serve as a temporary storehouse to replenish the supply of skin xanthophyll, which is esterified and seems to be relatively stable and permanent; c. It does not secrete the pigment into the rectal lumen to be eliminated with the feces; d. It is apparently not an organ specially equipped with an oxidase enzyme for destroying the xanthophyll; e. Its function may be that of a temporary repository of unesterified xanthophyll, which readily loses its pigment when a xanthophyll-rich diet is withheld. 8. Whether this excess xanthophyll is gradually excreted through channels other than the anus, or whether it is gradually destroyed (oxidized ?) in the blood, the authors are unprepared to decide at the present time.