IX. 9 



COLOUR OF FISHES 



257 



striping probably making the animal less conspicuous in disturbed 

 water than it would be if of uniform colour. The white under-side also 

 serves to lessen any shadows, an important factor for animals that live 

 in shallow water; similar shading is used by land animals. 



Fig. 153. Colour patterns of various tropical fishes. 



A, Muraena {Gymnothorax); b, bat-fish (Platax); c, butterfly fish (Holacanthus); n, butterfly 



fish {Cliaetodon); e, perch (Grammistes). (From Norman.) 



Devices of spots and stripes are found on fishes that live against a 

 variegated background (Fig. 153). The beautiful red and brown mark- 

 ings of a trout are a good example. Flat fishes, living on sandy or 

 gravelly bottoms, adopt a spotted pattern, which gives them a high 

 degree of protection, and we shall see later that they are able to change 

 colour to suit the ground on which they rest. The brilliant colours 

 of many tropical fishes probably serve mainly to break up the outline, 

 though no doubt the surroundings in which they live are also brilliant. 

 Great variety of colours may be found on a single fish, especially in 



