MARINE VERTEBRATES : AMPHIBIANS : OCEAN BED 



alter. Alteration of colour is due to contraction and expansion of 

 chromatophores without any quantitative variation in the carotenoid 

 content of these cells. Girella nigricans on the other hand, which loses 

 xanthophylls in captivity, tends to lose them more quickly on a white 

 background than on coloured backgrounds. Much more is known of 

 carotenoid distribution and function in the chromatophores of fresh 

 water than of marine fish ; this is discussed on p. 206. 



Owing to the wide distribution of carotenoids in fish tissues, Wald * ^ 

 does not consider their presence in some retinae of overwhelming 

 significance, although there is a possibility that they increase visual 

 acuity by reducing chromatic aberration and glare. * ^ 



(b) In Reproduction. As in all other animals so far discussed the 

 diflFerential mobilization and distribution in fish gonads is suggestive 

 of a specific function, but no such function has as yet been definitely 

 established. 



Both sexes of Cyclopterus lumpus^^ mobilize astaxanthin from the 

 liver to the skin and flesh during the summer spawn, and female 

 Fundulus parvipinnis ^ ^ transfer free xanthophylls to the ripening eggs 

 whilst the males increase the xanthophylls in their skin. Similar 

 appearances of free xanthophylls in ova have been noted in Ammo- 

 dytes tobianus ^ ® and Salmo salar. ^ * 



As with the problem of phototropic responses, the problem of 

 carotenoids in reproduction has been much more fully investigated in 

 fresh water than in marine fish. A full discussion of the problem is, 

 therefore, postponed until Chapter VII. 



MAMMALS 



Of the two main groups of whales, the Odontoceti (toothed whales), 

 which subsist on " Krill " (small Crustacea), would be more likely to 

 contain carotenoids than the Mystacoceti (whalebone whales) which 

 subsist on larger prey such as seals and smaller whales. 



Drummond and MacWalter, ^^ however, demonstrated that faeces 

 of a Krill-eating whale were very rich in astaxanthin. This suggested 

 that the pigment is probably not absorbed to any appreciable degree 

 and this probability is emphasized by the fact that Burkhart, Heilbron, 

 Parry and Lovem ^ ^ only very occasionally encountered astaxanthin in 

 whale body oils ; further Barua and Morton ^ ^ in a wide investigation 

 have never encountered whale liver oils containing astaxanthin, but 

 Schmidt-Neilson et al. ^ ** do report observing red oils from blue-whale 

 livers. Burkhart et al.y^^ however, consider the pigmentation of whale 

 oils to indicate a pathological condition. 



197 



