104 SALMON AND TKOUT IN ALASKA. 



The sockeye profits by its lake habit. Aii unoccupied food supply 

 is thus made available, and protection for the immature young is 

 obtained in waters not naturally inhabited b}^ many predaceous 

 animals. In basins of large productiveness the overflow of fry, 

 migrating as such, conserves the lake food suppl}^. In the main the 

 species secures immunity from disturbance on the spa\\Tiing beds, 

 passing beyond all but coho and king and avoiding the latter by 

 selection of colder water. 



CHANGES INCIDENT TO MATURATION. 



The changes that are associated with maturation of the reproductive 

 element vary in extent in the sexes, in the species, and with the age. 

 The production of the jaws and growth of canine teeth that is more 

 or less characteristic of all male salmons is seen also in the trout 

 and the charr. The change in body form — the increase in depth by 

 the ridging of the back — is much more developed in the salmon. The 

 changes seem to be greater in the larger, and presumably older, fish. 

 The grilse of the king show very little of it, scared}^ more than the 

 female, and in the case of iingerlings in the Sacramento which develop 

 mature spermatozoa there is no evident external change. 



In the trout and charr the upper jaw elongates somewhat but does 

 not become hooked. The lower jaw elongates and becomes knobbed 

 or hooked ; this swelling is usually received in a corresponding recess 

 or notch in the upper jaw, but sometimes is sufficiently large to 

 prevent complete closure of the mouth. After the spawning season 

 is over these growths are to an extent resorbed, but the jaws never 

 fully recover their original shape. 



In the Sacramento the king salmon of the spring run show none of 

 these characters until some time after entering the fresh water. The 

 late runs, being more developed, show some changes by the time they 

 have reached the mouth of the river in Suisun Bay. The various 

 changes, which have been fully described by Rutter, are progressive 

 ^vith the development of the reproductive elements. Little of the red 

 color is shown by this species except in the large (old ?) males, and 

 even in these never approaches the brilliancy of the sockeye or coho. 

 Neither do they as fully develop the body depth as species which 

 frequent shallower waters. 



The Alaskan sockeye at the time it is first taken in the fisheries has 

 already begun to show the hooked jaw, so that with care one can 

 distinguish the sexes in the larger fish. Cases will occur, however, in 

 which the female has jaws somewhat prolonged, and there are cor- 

 responding cases of males with neat heads, so that in statistical work 

 it is essential that the fish be opened to make sure of the sex. Late in 

 the season, or in occasional schools at any time, the males are more 

 readily distinguishable. 



