In addition to all the wonderful devices of 'fixed adaptive color and pattern 

 worn by fishes, they have often the extraordinary gift of 'chameleonism,' 

 i. e., quick, sometimes instantaneous, color-change. Indeed, some of them 

 have this power in a higher degree than any other vertebrate animals known 

 to man, their coloration being as it were 'alive,' and 'fluid' — darkening 

 and brightening, and shifting its pattern, in swift, repeated mutation. Some- 

 times the changes are evoked only, or chiefly, by changes in the light which 

 strikes the fish's surface. But no doubt the chief use of such changeableness 

 of coloration, in most cases, is adaptability to various backgrounds. The 

 fishes most subject to such 'chameleonism' are the gay-colored 'ground- 

 haunters' of tropical seas, — the very ones that are notable for their lack of 

 iridescence; — but trout and probably other fresh- water fishes are also some- 

 what 'chameleonic' Mr. A. R. Dugmore, in his admirable and delightful 

 book on Nature photography ("Nature and the Camera"), gives some inter- 

 esting testimony on the subject. He, moreover, fully and clearly states the 

 fact that even the gaudiest tropical fishes are colored for concealment. But, 

 like all the rest, he ignores the great basic principle of obliterative counter 

 shading, without whose aid the color adaptation would be of so little avail. 



So far we have considered mainly the fishes of salt water. But of course 

 the same general principles, with various small modifications, apply to fresh- 

 water fishes — the inhabitants of lakes and brooks and rivers. Some of those 

 I have already mentioned, such as the salmon and the herring, live in both 

 kinds of water, making annual migrations from the one to the other and back 

 again. These are all of the free-swimming type — ^with colors and markings 

 not specialized to match any one sort of ground, but rather adapted for gen- 

 eralized wa/er-picturing near the surface. This, the type of coloration of the 

 generality of free-swimming "pelagic" fishes, is also, with modifications, that 

 of the free-swimming fresh-water kinds — much more localized in habitat 

 though they almost always are. Inland 'bottom-fish,' also, are much like 

 marine ones, though with less variety of coloration. Some of them are ' mud- 

 fishes,' and colored muddy brown or gray, with full obliterative shading, 



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