CAROTENOIDS 



of vitamin A itself; furthermore, the technique used to prepare 

 astacin, which was inactive, would also remove any vitamin A originally 

 present. 



Assuming then that astaxanthin is inactive, three possibilities 

 remain (i) zooplankton contain pre-formed vitamin A, (ii) fish can 

 synthesize vitamin A de novo or (iii) vitamin A precursors, as yet 

 unidentified, are utilized by fish and exist in zooplankton. 



All the evidence we possess on all other animal species points away 

 from the last two possibilities. They must, therefore, be considered 

 extremely unlikely to function in fish. This is in spite of the fact that 

 recently Lane'^ has claimed to have separated the vitamin A activity 

 of zooplankton {Temora turbinata and Centropages typians) from their 

 carotenoid fraction. The vitamin A-active fraction, which had an 

 absorption spectrum with a maximum at 310 mfx., when fed to the fish 

 Limanda ferruginea^ resulted in the accumulation of vitamin A 

 (X-max. 325m(x.) in the liver. The conclusion that non-carotenoid 

 material can be utilized as a vitamin A precursor, must be accepted 

 with considerable reservation, pending much more rigorous demon- 

 stration of the purity of Lane's active fraction. The presence of con- 

 siderable amounts of impurities in material containing vitamin A in 

 small amounts could easily displace the absorption maximum to shorter 

 wavelengths. 



The first suggestion has always seemed the most likely, but it is only 

 very recently that evidence has been obtained which has transformed 

 it into a certainty. It will be interesting to follow chronologically the 

 investigations leading up to this conclusion. 



Drummond and Gunter's ' * pioneer studies showed that zooplankton 

 oils from mixed copepods and Calanus finmarchicus exhibited very little 

 vitamin A activity, contained no pre-formed vitamin A and only small 

 amounts of p-carotene ; phytoplankton oils from Chaetoceros spp. and 

 Lauderia borealis exhibited slightly more activity by virtue of their 

 higher p-carotene content, for no preformed vitamin A could be 

 found. 



In spite of a careful study completed in 1939 by Gillam, El Ridi and 

 Wimpenny, « ^ the problem still remained unresolved. The gross plank- 

 ton hauls investigated by Gillam et al. showed the presence of both 

 vitamin A and carotene. As the most prolific compounds of the phyto- 

 plankton fraction, Rhizosolenia styliformis and Biddulphia sinensis con- 

 tained no vitamin A, it would not have been unreasonable to assume 

 " by difference " that the vitamin A was located in the zooplankton. 

 Against this is their observation that the preformed vitamin A content 

 was maximal well before the zooplankton population was densest. 



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