24 BRITISH FRESHWATER FISHES 



certainly place them first on account of their size, 

 beauty, and activity, whilst the naturalist finds endless 

 scope for work in the solution of the problems con- 

 nected wnth their life-history and distribution, and in 

 the attempt to distinguish and define the numerous 

 races and species. 



The Salmonidae are fishes with a naked head and 

 scaly body, which in form and appearance are more 

 or less similar either to a Trout or a Herring. 

 The non-protractile mouth is bordered above by the 

 praemaxillaries in front and the maxillaries at the 

 sides ; the fins have no spinous rays ; the pectorals 

 are placed low and the pelvics far back, below the 

 dorsal, which is in about the middle of the length of 

 the fish ; the presence of an adipose fin, a small 

 fleshy flap on the back above the end of the anal 

 fin, is an important character common to all the 

 members of this family, whilst the absence of oviducts 

 is a peculiarity worthy of mention. 



The Salmonidae are found in the arctic and 

 temperate regions of the Northern Hemisphere, and 

 may be regarded as marine fishes which are estab- 

 lishing themselves in fresh water; there are many 

 permanently fluviatile or lacustrine forms, but a 

 number of others spend a considerable part of their 

 life in the sea, and in some cases non-migratory and 

 migratory fish occur within the limits of one species. 

 Some writers look upon the Salmon and its relatives 

 as true freshwater fishes which have acquired the 

 habit of going to the sea for food, and which return 

 to their original home to spawn. Against this it 

 may be urged that whereas many marine fishes take 

 to fresh water, the reverse is a rare phenomenon ; to 

 illustrate the former we may instance the Bass 



