ANIMAL CAROTENOIDS 



may have been operating. Such factors would include the effect of 

 photo-environment on absorption and retention of carotenoids, egg 

 laying, and temporary sparing of carotenoids by drawing on other food- 

 stuffs. It is now generally assumed that specific carotenoids such as 

 astaxanthin are produced by oxidation of the ingested carotenoids, 

 but which carotenoid is the precursor is unknovm (but see p. 225). • ^ 



Function 



A sexual function is suggested by the accumulation of carotenoids 

 in the gonads but further than that it is impossible to go. Abeloos and 

 Fischer ^ ^' ^ ^ found that in gravid female Cardnus maenas the hepato- 

 pancreatic stores are transferred to the ovaries via the blood stream. 

 Goodwin ^°^ has recently shown that during the development of 

 lobster eggs astaxanthin is not utilized in any way. 



The free pigment is, however, liberated from its protein complex 

 (ovoverdin) a week or so before hatching. 



IMPORTANCE OF ZOOPLANKTON CAROTENOIDS AS 

 A SOURCE OF PROVITAMIN A FOR FISH 



The main sources of foodstuffs for fish which contain large amounts 

 of vitamin A in their liver and intestinal wall are the zooplankton. 

 Copepods make up the ** permanent " source of zooplankton whilst 

 the eggs and larvae of fish and invertebrates make up the ** transitory " 

 source. ^ ^ Phytoplankton are utilized to a lesser extent. 



Copepods live on diatoms which contain small amounts of [3 -carotene 

 (the chief vitamin A precursor (see p. 269) ), but whose chief pigment is 

 fucoxanthin. Copepods apparently convert these diatomic carotenoids 

 into their characteristic pigment astaxanthin and store only minute 

 amounts of p- carotene. About the same relative pigment distribution 

 is noted in eggs and larvae. Phytoplankton contain probably a little 

 more (3-carotene than do zooplankton. 



It had long been realized that the amounts of p-carotene available 

 in zooplankton were insufficient to account for the large amounts of 

 vitamin A accumulated by plankton-feeding fish. It has been suggested 

 that astaxanthin might conceiveably be a vitamin A precursor in fish; • ^^ 

 on general grounds this must be considered highly improbable (see 

 Chapter 12) even though it has been claimed that astaxanthin isolated 

 from the shrimp, Aristeomorpha foliacea (=Penaeus foliaceus), is 

 vitamin-A active. '^^ The main objection to this work is that no 

 account was taken of the possible presence in the astaxanthin fraction 



173 



