FRESH WATER ANIMALS: DEPOSITS: AMPHIBIA 



was named erythropterin. Platypoecilus and Xiphophorus varieties 

 carrying the gene which controls red pigmentation, possess a hybrid 

 chromatophore which Goodrich et al. term a xantho-erythrophore ; 

 in this cell are concentrated both the carotenoids and erythropterin. 



Steven 2. 12 ^^s also obtained evidence that carotenoids are con- 

 nected with the chromatophore system by his work on trout and lam- 

 preys, but found that xanthophores contain only lutein whilst the red 

 pigment of the erythophores is not erythropterin but astaxanthin {see 

 Table 36). The cause of this difference is erythrophore pigmentation 

 in different species is an interesting problem for further investigation. 



It remained, however, for Steven to provide the quantitative evi- 

 dence which quite clearly demonstrated that in trout lutein and asta- 

 xanthin are associated with the xanthophores and erythrophores 

 respectively. He showed that the red spots of the skin contained about 

 twenty times as much astaxanthin as did the regions which did not 

 contain any yellow spots. With the aid of a micro-spectrophotometer 

 he measured the absorption spectra of single chromatophores and 

 found that the xanthophores and erythrophores exhibited spectra 

 corresponding quite closely with lutein and astaxanthin respectively. 

 It was estimated that a single xanthophore contained 11-28 10" • (xg. 

 of lutein and a single erythrophore 200-340 10"^ [jig. of astaxanthin. 



Further evidence of the association of carotenoids with the chrom- 

 atophores of S. trutta came from dietary studies. After nine months 

 on a carotenoid-frec diet, yearling fish exhibited pale-yellow xantho- 

 phores, generally distributed over the skin and fins, and a very few 

 orange-pink erythrophores mainly situated at the tip of the adipose 

 fins ; the erythrophores which generally accumulate along the lateral 

 line had disappeared. These observations agree with the quantitative 

 studies (Table 37) which demonstrated the presence of small amounts 

 of lutein and no astaxanthin in these fish. 



Steven's studies on the metabolism of carotenoids during the 

 reproductive cycle of trout also indicate the close relationship between 

 these pigments and chromatophores. Muscle carotenoids, but not 

 skin (chromatophore) carotenoids are mobilized into the developing 

 ovaries. During larval development lutein and astaxathin are not 

 utilized, but are quantitatively transferred in constant ratio from yolk 

 to embryo ; during this process they are esterified and accumulate 

 in the skin and fins. This rate of transference follows much more 

 closely the increase in length of the posterior end of the developing 

 embryo than the overall growth, measured either as length or weight. 

 As the majority of the carotenoid-containing chromatophores develop 

 in the skin of the posterior end of the body, especially in the tail and 



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