JAN. CHANGE OF COLOUR IN TROUT. 177 



swim. When fresh water is put in they always come 

 to the place where it is poured, and seem to look for 

 any particles of food or any insects that may come 

 in with it. They feed on worms which the boys 

 often bring them, and which they take immediately, 

 without fear. The change of colour in fish is very 

 remarkable, and takes place with great rapidity. 

 Put a living black burn trout into a white basin of 

 water, and it becomes, within half an hour,* of a light 

 colour. Keep the fish living in a white jar for some 

 days, and it becomes absolutely white ; but put it 

 into a dark-coloured or black vessel, and although on 

 first being placed there the white-coloured fish shows 

 most conspicuously on the black ground, in a quarter 

 of an hour it becomes as dark coloured as the bottom 

 of the jar, and consequently difficult to be seen. 

 No doubt this facility of adapting its colour to the 

 bottom of the water in which it lives, is of the 

 greatest service to the fish in protecting it from its 

 numerous enemies. All anglers must have observed 

 that in every stream the trout are very much of the 

 same colour as the gravel or sand on which they 

 live : whether this change of colour is a voluntary 

 or involuntary act on the part of the fish I leave it 

 for the scientific to determine. 



* In the case of some fish the change is perceptible in five 

 minutes. 



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