MARINE vertebrates: AMPHIBIANS: OCEAN BED 



Fundulus parvipinnis is outstanding ; aquaria-kept Fundulus were 

 divided into three groups fed respectively, a carotene diet (beach w^orm 

 Thoracophelia mucronata), a xanthophyll diet (garibaldi, Hypsypops 

 rubicunda) and a carotenoid-free diet (flesh of Californian halibut, 

 Paralichthys calif ornicus). On the first two diets the Fundulus carotenoid, 

 entirely taraxanthin-like, increased in both concentration and absolute 

 amounts although the increase was much greater on the xanthophyll 

 diet, whilst in the third group there was a drop in concentration but no 

 change in total amount. This experiment makes it clear that Fundulus 

 cannot synthesize carotenoids de novo but that they do have the ability 

 to oxidize carotenes to xanthophylls. 



In the case of Hypsypops rubicunda^ however, a diet containing only 

 (3-carotene did not allow the animals to maintain their normal xan- 

 thophyll content, although some ^-carotene was stored in the skin. 

 This latter observation is of special interest because it is the first time 

 that it has been possible experimentally to produce storage of [3- 

 carotene in the skin of fish. ^^^. 



Observations on surf perch (Cymatogaster aggregatus) also show that 

 carotenoids are not metabolized in the same way in all fish. ^ • When fed 

 the red shrimp {Hippolyte californiensis) which contains p-carotene and 

 neutral (? taraxanthin) and acidic (? astaxanthin) xanthophylls, Cymato- 

 gaster only utilizes the neutral xanthophyll ; the other two pigments are 

 excreted quantitatively. After hydrolysis in the lumen the taraxanthin 

 was esterified, presumably as it passed across the gut wall, and trans- 

 ported to the skin, where, in the sexually inactive fish, it remained 

 in constant amount. Excess taraxanthin was stored unesterified in the 

 rectal segment of the gut ; it rapidly disappeared from this site when 

 food was withheld. The dietary astaxanthin esters although hydrolysed 

 in the gut were not absorbed. The function of the xanthophylls 

 stored in the rectal segment is somewhat obscure but the following 

 facts were established : 



{a) the segment does not absorb carotenoids directly from the 

 lumen but is provided with them from the blood stream ; 



{b) it neither excretes xanthophylls into the rectal lumen nor oxidizes 

 them in situ ; 



{c) it is not a temporary storehouse for replenishing skin carotenoids. 



The concentration of xanthophylls in the skin of Hypsypops rubicunda 

 increases with age {see Table 34). This is in agreement with the colour 

 changes observed in the developing fish, i.e., from the dull orange of 

 the half-grown specimens to the brilliant orange adults. ^ ^^ 



Some fish appear to make little or no use of their dietary carotenoids 



195 



