COLOUR OF FISH SUITED TO THE WATER. 7 



food, and increase rapidly in size as a consequence of the 

 easy life they lead : for it is a well-authenticated fact, that 

 fish which have to toil hard in hunting for their food are 

 bony and ill-conditioned, and never fat. Another strange 

 characteristic of the finny tribe is, that on changing their 

 locality they assume a colour suited to the waters to which 

 they have migrated, the result, probably, of the altered 

 condition of light or electricity they have undergone in 

 making this change : so that fish bred in a dark or deep 

 water are dark, and those in a clear, bright, and shallow 

 stream are light arid brilliant, and hardly discernible 

 therein. 



A friend at Dorking asked me why it was that he could 

 not breed trout, or indeed any fish, in one of his streams, 

 although when he placed the fresh brood therein they grew 

 rapidly ; whilst in a second stream they bred, but did not 

 thrive ? My explanation was, that in the one stream the 

 corruption to which the water was liable destroyed the egg, 

 but afforded the brood abundance of food ; whilst in the 

 other, there being very little food, the fish had to work hard 

 to obtain it, and were thus kept lean and small. 



In proof of the extraordinary growth of fish when con- 

 fined and regularly fed on food fit for them, I may refer to 

 the two electric eels (Gymnoius electric us), now exhibiting 

 at the Polytechnic Institution. These fish were imported 

 six years back, and placed as objects of curiosity in the 



