OXYGEN NECESSARY TO SALMON 163 

 fresh water for no other purpose than to shed 

 their spawn, and during the interval of waiting 

 they are doing, practically, nothing — ^merely 

 waiting for the ova (and sperm) to mature. 

 But to this end oxygen is highly necessary, 

 therefore we observe the fish lying mostly in 

 the heavy, aerated streams ; but as the water 

 gets low and becomes stale and tepid, the fish, 

 now and again, is compelled to come to the 

 surface and obtain air from the outside. I 

 make this statement with some assurance, as 

 I have been in a position to see a chain of air 

 bubbles rising from the depths which could 

 not be confused with scattered bubbles result- 

 ing from the splash of the fish as he plunged. 



In highly aerated waters, such as the snow- 

 fed streams of Norway, salmon show less on 

 the surface, though probably there are more 

 fish contained in these rivers. 



When creatures, either from lack of food, 

 climatic conditions or for other reasons, are 

 forced to " weather " a certain period, they 

 become inactive and pass into the state known 

 as " hybernation " or " aestivation," as the 

 case may be, when they rest in a torpid or 

 semi-torpid condition until nature is again 

 ready for them to resume active life. This, in 

 my belief, is the salmon's case. Shortly after 

 entering fresh water the fish lapses into this 



