26 OBSERVATIONS ON A SALMON RIVER 



cold water, or the fish may not have be- 

 come accustomed to the somewhat sudden 

 change from salt to fresh water, for I have 

 no doubt that they are affected as a man 

 from the lowland would be who suddenly 

 found himself in a high altitude. 



A very interesting experiment was tried 

 in Scotland in 1906. "Two grilse were 

 taken from a net in the Bay of Nigg and 

 placed in sea water in a tank at the fish 

 hatchery for the purpose of discovering 

 how long sea lice will remain attached to 

 salmon in fresh water. The density of the 

 water was reduced by allowing fresh water 

 to enter. This operation was regulated so 

 as to represent approximately in time the 

 period of one flood tide. The fish showed 

 considerable distress at first, from which it 

 is natural to suppose that the transference 

 to brackish water was too rapid. 



"Dating from the time the water was 

 quite fresh the sea lice remained on one 

 fish for four days and on the other for five 

 days." (Calderwood.) 



