vi COLORATION I 7 1 



probably by a rat or a cat, the dark bands were permanently 

 retained. 



Changes of coloration sometimes take place, which either have 

 no discernible relation to age, condition, or surroundings, or are 

 brought about by domestication; and in individuals of the same 

 species there is often a wide range of colour- variation, which is 

 sometimes, but not always, associated with particular localities. 

 In some fresh-water Fishes a yellow colour may replace the 

 original tint (xanthochroism). The usually dull greenish Tench 

 (Tinea vulgaris) occasionally becomes a bright orange -yellow. 

 Another Cyprinoid, the common Gold Fish (Cyprinus auratus), in 

 its wild state in China is also a dull brown or green, but, when 

 domesticated, assumes in the first year of its life a black colour 

 (melanism), then a silvery hue, and finally the vivid ruddy golden 

 colour of the adult ; occasionally, but rarely, the Fish is an 

 albino. 



The value of a particular coloration in Fishes, either as an aid 

 to concealment and protection from enemies, or by enabling them 

 to secure their prey, may now be illustrated by a few examples. 



As previously shown, the colours of Fishes may be artificially 

 varied according to their surroundings. Changes of a similar 

 kind occur naturally, and when they tend to assimilate the tints 

 of the Fish to the prevalent hues of its surroundings, and con- 

 sequently aid concealment, we have examples of what has been 

 termed variable protective resemblance. Individuals of the same 

 species vary in colour according to the opacity of the water they 

 live in, becoming darker in muddy or peaty water, and brighter and 

 lighter in shallower or clearer water. Trout caught in a stream 

 with a gravelly or sandy bottom are lighter in colour than those 

 obtained from a muddy stream, and it is well known that the 

 same Fish changes colour as it passes from the one background to 

 the other. 1 In a lake in County Monaghan, Ireland, the Trout are 

 darker on that side which is bounded by a bog, but are of the 

 beautiful and sprightly variety generally inhabiting rapid and 

 sandy streams on the opposite side where the bottom is gravelly ; 

 and narrow as the lake is, the two kinds of Trout appear to con- 

 fine themselves to their respective areas. 2 Trout obtained from a 



1 Poulton, The Colours of Animals, Internat. Scientific Series, London, 1890, 

 p. 82. 



2 Percy St. John, quoted by Day, Fishes of Great Britain and Ireland, London, 

 1880-84, ii. p. 58. 



