GRILSE 47 



scales of the fish as secondary and more or less 

 accidental results of his visiting the sea and feeding 

 there. We admit that he thrives surprisingly in 

 the sea for a fresh water fish, but we know he can 

 spawn only in fresh water, and ask how can he be 

 a marine fish if he cannot propagate his species in 

 the sea. Do we call the common eel a sea fish 

 because it spawns in the sea ? We call it the fresh 

 water eel. Is the shad a fresh water fish because 

 it spawns in rivers ? In my view, the prevailing 

 characteristics of the group of fishes to which the 

 salmon belongs are those of marine fish of plastic 

 nature, capable of much local variation both of 

 appearance and habit, many of which enter fresh 

 water freely. The fry exhibit a strong impulse to 

 descend the rivers of their birth and to enter the 

 sea ; they do not develop into normal or healthy 

 adults if they are retained forcibly, nor under usual 

 conditions do they come to sexual maturity unless 

 they have visited the sea. In some localities where 

 great lakes occur a degenerate race becomes possible, 

 but these land-locked salmon cannot be regarded as 

 representatives of what the salmon used to be ; 

 they are not the fish through which evolution could 

 proceed. It is quite possible that Brachymystax, 

 the large salmonid of the Siberian rivers and Lake 

 Baikal, which viewed systematically comes between 

 Salmo and Coregonus, may be a migratory fish 

 which remains in fresh water for longer periods 

 than our salmon, and which in its great size and 

 full development differs in this respect from the so- 

 called land-locked salmon, but the life history of the 



