62 BRITISH FRESHWATER FISHES 



brackish or salt water, and this may be true of 

 many of them ; in fact, they are intermediate in 

 appearance and habits between River-trout and 

 Sea-trout. Fish of this type are found in the 

 brackish waters of Loch Stennis in the Orkneys, 

 where they attain a large size, and have been 

 described under the name Salmo orcadensis. 



We now come to the non-migratory freshwater 

 Trout, and it is among these that we should most 

 expect to find distinct forms, especially in isolated 

 localities. However, after a careful examination of 

 a large number of examples from all parts of the 

 British Isles, I find a remarkable variability in those 

 features which are easily influenced by habits or 

 environmental conditions, but a no less remarkable 

 constancy in those which are not so affected. 



The size attained differs enormously in different 

 localities ; for example, in Lough Neagh, the largest 

 lake in the British Isles, Trout of 30 lbs. used to 

 be quite common, and they are said to grow to as 

 much as 50 lbs. in weight; on the other hand, the 

 Trout of some of the mountain streams in Wales or 

 Cornwall average only 2 or 3 ounces, and rarely 

 grow larger. The size is dependent to some extent 

 on the volume of water and the amount and nature 

 of the food available ; an important factor also is 

 the number of fish, which depends on the area 

 of the breeding-grounds and the extent to which 

 enemies of the fry and young fish flourish. I have 

 caught a good many Trout in quite a small stream 

 in Dorsetshire, where the usual size is from 

 I to 3 lbs., but where I have never taken more 

 than four in a day. Here I believe that so few 

 young fish escape the perils that beset them in the 



