CAROTENOIDS 



adipose fins, this correlation indicates that the rate of transfer of pig- 

 ments is related to the development of the cells which receive them. 



Making use of an ingenious technique, Steven managed to remove 

 about 90 per cent, of the yolk carotenoids from the newly hatched trout 

 larvae. Fish treated in this way developed normally on a carotenoid- 

 free diet of the oligochaete worm Enchytraeus, with the exception that 

 they were very pale in colour and completely lacking in both xantho- 

 phores and erythrophores. 



It seems then that a major reason for the mobihzation of carotenoids 

 into the ova is to ensure that the newly-hatched larvae are adequately 

 equipped with chromatophores. The most interesting question which 

 remains to be answered is why, in salmon as well as trout, are the 

 xanthophyll esters saponified during their transference to the eggs ? 

 The presence of free xanthophylls in the eggs suggests ,by analogy 

 with vitamin A, that the pigments are " metabolically "* as well as 

 *' physically " functional, because the functional form of vitamin A is 

 probably the free vitamin (but see p. 271), whilst the esters are the 

 storage form. This possibility will be considered in the next section. 



Steven * ^ has recently observed that lampreys (Lampetra palneri and 

 L. fluviatilis) accumulate lutein in the non-expandible lipophores in the 

 dermal and subdermal layers of the skin (see also p. 203), but that they 

 play no part in coloration. 



In Reproduction 



In spite of the proof by Steven that carotenoids are not needed for 

 the normal embryonic development of brown trout, the work of 

 Hartmann et al.^^^ on rainbow trout indicates that they may be meta- 

 bolically functional and of importance in the fertilization process rather 

 than in embryonic development. They report that astaxanthin acts 

 as a fertilization hormone, gamone I (Gj). Two gamones, Gj and Gn 

 occur in trout eggs and the ovarial fluid surrounding them. Two 

 natural antagonists Aj and An occur in spermatozoa. Astaxanthin, 

 P-carotene and lutein all have some positive effect on motility of 

 spermatozoa, whilst astaxanthin and ^-carotene, but not lutein, have 

 a positive chemotactic action on the spermatozoa ; ^-carotene is, how- 

 ever, much less active than astaxanthin. Astaxanthin is, however, the 

 only pigment which effectively antagonizes the naturally-occurring 

 androgamone I ; it is thus concluded that astaxanthin is a true fertiliza- 

 tion hormone. 



It must be emphasized that in this investigation no proof was 



* A distinction must be drawn between a possible ** metabolic " function and 

 a " physical " function, such as participation in photo-responses which could 

 be carried out by the esterified pigments. 



208 



