46 MARVELS OF FISH LIFE 



least, there are the numerous " white fishes " which are 

 present in every lake and river throughout North 

 America. The white fishes differ from other salmonoids 

 in having large scales and delicately shaped mouths ; 

 the best known representative of this group in our 

 country is the pollan of Irish waters. It is well to 

 remember that in America the term " white fishes " 

 applies to these large-scaled members of the salmon 

 family ; but at home it refers to the silvery section of 

 the carp family, such as the roach, rudd and dace. 

 Though the salmons are of great importance as a food 

 supply throughout the northern hemispheres, yet it is 

 mainly as a sporting fish that they appeal to civilised 

 man. 



Until recently the brown trout, the Loch Leven trout, 

 the Great Lake trout (Salmo ferox) and others have been 

 described as different species of the salmon family ; but 

 these fish are merely varieties of the common brown 

 trout (Salmo fario). The variations in size and appear- 

 ance are due to alterations in environments and in feed- 

 ing habits. 



Further, the completeness with which the brown trout 

 can acquire the appearance and habits of a migratory 

 salmonoid suggests that at no very distant date the sea 

 trout, and possibtythe salmon itself, was a brown trout. 

 The facts in support of the suggestion that the various 

 trouts, migratory and otherwise, and possibly the salmon, 

 have a common ancestor in the brown trout, are as 

 follows : — 



