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 possibly the 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 :— 
