American Fisheries Socieiy 95 



ally lost and are replaced in part at least by the fresh water in- 

 truders. The parasitic fauna of the Tay salmon becomes thus 

 altered during its migration but is not so greatly reduced in 

 numbers as in the case of the salmon from the Rhine. 



These observations upon the Atlantic salmon in different 

 streams indicate clearly that as a certain individual it is char- 

 acteristic of the parasitic fauna of the same host taken in differ- 

 ent localities. This fact seems to have escaped emphasis at least 

 at the hands of ])rcvious investigators. They have been most 

 strikingly impressed l)y tlic fact that the parasitic infestation 

 reaches the minimum when after spawning this salmon starts 

 on its return to the sea. Elsewhere I have called attention to 

 the interesting biological parallel between the later condition 

 and that of the hibernating frog and marmot. In general one 

 may say that tlie reproductive period constitutes the terminus 

 of a physiological cycle and the host starts on its new cycle un- 

 incumbered by the parasitic guests of a former period. 



In view of these interesting results from the investigation of 

 parasitism in the European sahnon you will understand with 

 what pleasure I accepted the courteous invitation of Commis- 

 sioner Bowers to investigate the ]iarasitic diseases among the 

 Alaska salmon. While tlie P^uropean work was all done on a 

 single species, Salmo salar, in which local races or varieties are 

 recognized by some students, the Pacific salmon appears in five 

 species of more or less common occurrence and commercial im- 

 portance: the King sahnon (Oiteliurli j/nrli us tschawytscha) : the 

 Bed salmon ( (hiclioi-ln/nchns nerha) ; the Cohoe or silver salmon 

 (Onchorhi/iirli us kisiddi ) : tlie Humpback salmon (Onchorhyn- 

 ciuis (/orhusclid ) : and the Dog nv Calico salmon (Onchorhyn- 

 chus l.-eta )■ In my work esi)ecial attention was paid to the Alas- 

 ka or Red salmon whicli is the most al)undant and most impor- 

 tant commercially of those species in the Ketchikan district in 

 which I was located. A total of one hundred and thirty-eight 

 specimens of this fish from various ])ortions of the district were 

 examined from the time at which the fish appeared early in 

 June np to the time of spawning about September 1. The ma- 

 terial examined included such as was taken from salt water and 

 also specimens from fresh water lakes at different periods of 

 time so that the series would give a reasonable view of the con- 



