522 THE BIOLOGY OF MARINE ANIMALS 



closely artificial backgrounds made up of regular black and white areas. 

 On the skin of the fish, areas appear similar in size and shape to the back- 

 ground, without, however, any actual reproduction of the figures (Fig. 

 11.9). Moreover, on blue, green, yellow, orange, pink and brown back- 

 grounds the flounders become coloured in tones very similar to those of 

 the bottom. Red tints, however, are not accurately copied (Fig. 12.10) (54). 

 Other species with striking colour changes are the wrasse Crenilabrus 

 roissali, which appears in hues of blue, green, yellow and red ; and the 

 killifish Fundulus heteroclitus, which changes in shade from light grey to 



(b) 



Fig. 12.10. Changes in the Chromatophores (Melanophores and Xantho- 

 phores) of the American Flounder or Gulf Fluke Paralichthys albiguttus, 



on Different Backgrounds 



Guanophores, cross-hatched; xanthophores, stippled; melanophores, solid black. 

 (a) Two regions from a specimen on a white background ; (b) specimen on a black back- 

 ground; (c) specimen on a yellow background. (Redrawn from Kuntz, 1917.) 



dark, and assumes tints of pink, yellow, green or blue on appropriate 

 backgrounds. Light and dark neutral tints result from contraction and 

 expansion of melanophores ; whereas matching of coloured backgrounds 

 involves appropriate movements of erythrophores and xanthophores, and 

 the interplay of light effects from the guanophores as well. In Fundulus 

 heteroclitus, for example, the yellow chromatophores partly expanded over 

 the blue guanophores of the stratum argenteum give the green colour seen 

 in fish which have been retained on a green background. In fish kept on 

 blue backgrounds the xanthophores are maximally contracted, revealing 

 the blue stratum argenteum beneath. Similar histological transformations 

 have been described in the flounder (Fig. 12.10). 



