COLOUR CHANGES 



521 



condition the melanophores appear as dark spots, but when expanded they 

 assume a variety of radiate and stellate shapes which are characteristic of 

 each species. Other kinds of chromatophores show similar peculiarities of 

 form (Fig. 12.2) (29, 54). 



Perhaps some of the most striking colour changes among teleosts are 

 to be seen in certain tropical reef fishes such as the sea-perches {Epine- 

 phelus), which have a whole series of colour phases, and can switch from 

 one to another in the course of a few minutes. The Nassau grouper E. 

 striatus has eight different colour liveries which vary from one very dark 

 phase to one creamy white, and intermediate phases dark above, light 

 below, with variegated markings and bands in shifting patterns (Fig. 11.10). 

 These several colour phases have considerable cryptic value against the 



Epider 



Pigment cells 



Fig. 12.9. Section through the Skin of a Teleost, Based on the Pollack 



Gadus pollachius, to Show the Arrangement of Pigment Cells. 



(After Schnakenbeck, 1926.) 



multicoloured backgrounds of the coral reefs. Indeed Longley, in his 

 submarine researches, records how he was able to evoke different colour 

 phases in reef fishes by leading individuals, with offers of food, from one 

 kind of environment to another (24, 47, 67). 



Flat fishes (pleuronectids) are noteworthy for the complexity of their 

 colour responses, adapting the fish in colour, shade and pattern to its 

 background. As a result of these changes the animals are rendered well- 

 nigh invisible on the muddy, sandy or gravelly bottoms which they fre- 

 quent, and the resemblance is heightened by the tendency of the animals 

 to bury themselves partially in the substratum. In experiments carried out 

 with the Mediterranean flounder Bothus podas on backgrounds with various 

 checkerboard patterns, the fish were found to harmonize very closely with 

 the patterns used; colour changes, however, were restricted to the black, 

 brown, grey and white tints of its normal environment. More remarkable 

 is the American flounder Paralichthys albiguttus which simulates very 



M.A.— 17* 



