COLORATION 209 



In another form the blue on the head is wanting. In still 

 another the body is yellow and black, with blue on the head only. 

 In others the fins are plain orange, without checks, and the 

 body yellow, with or without blue stripes or spots and some- 

 times with spots of black or violet. In still others the body 

 may be pink or brown, or violet black, the fins all yellow, part 

 black or all black. Finally, there are forms deep indigo-blue in 

 colour everywhere, with cross-bands of indigo-black, and these 

 again may have bars of deeper blue on the head or may lack 

 these altogether." 



The apparently meaningless display of colour shades and 

 patterns exhibited by many fishes have for the naturalist a 

 deep, although not always obvious significance, but before 

 dealing with this matter it is important to be quite clear as 

 to the function of coloration. For the most part, the colours 

 of fishes, like those of any other animal, serve to conceal their 

 owners either from their prey or their natural enemies. This 

 is not always the case, however, for, as will be pointed out in 

 due course, in some fishes the colours serve a totally diflferent 

 purpose, and attem.pts that have been made to explain all 

 types of coloration in terms of concealment sometimes press 

 the matter to the point of absurdity. The fact remains, how- 

 ever, that in a very large number of fishes the particular hues 

 and patterns adopted do tend to render them invisible, or, at 

 least, very inconspicuous in their natural surroundings. A few 

 examples will suffice to illustrate the general principles of these 

 concealing colours. 



A Carp [Cyprinus) or Roach (Rutilus), or almost any other 

 fish to be found in our own rivers, exhibits a gradation of shades 

 from silvery or yellowish-white below to a dark-blue, green, or 

 brown above. This is known as obliterative shading, and is 

 exactly the opposite of that which would be produced by light 

 thrown upon the fish from above, and the general effect is to 

 destroy the appearance of thickness and make the fish appear 

 as a perfectly flat object. Seen from above against a background 

 of water and the bottom of the stream coloured more or less like 

 itself, the fish is almost indistinguishable at even a short distance, 

 while seen from below the belly bears a close resemblance to 

 the surface of the water and the clear atmosphere above. 

 Many fresh-water forms depend entirely on this simple shading 

 to bring about their concealment, but others enhance the 

 obliterative effect by the development of darker markings in 

 the form of bars, stripes, spots, and blotches of all kinds. The 



