American Fisheries iSociety 93 



ter representative of a great marine gTOup, the codfishes. Tlie 

 hiwver is parasitized by a few species found in hosts that are 

 confined to fresh water. On the other hand it shelters many 

 parasites that are characteristically frequent in marine fishes 

 and usually al)sent among fresh water hosts. Thus though a 

 time interval of unknown length has intervened between the 

 present and that period in whieli the Uiwyer established its fresh 

 water hal)it at yet it shelters ])arasitic forms which are char- 

 acteristic of its old associates and has acquired little new in- 

 festation from its fresh water home. The records might be mul- 

 tiplied but they indicate clearly tliat a study of parasitism will 

 yield valuable evidence to confirm or reject proposed hypotheses 

 with reference to tlie origin, migration, and hal)its of our fresli 

 water fish. It should accordingly be looked upon as a Ijiological 

 criterion of the most useful type. Tlie primary object of this 

 ])aper is to consider tlie side light which a study of its parasitic 

 fauna tlirows upon tlie migrations of the l*acific salmon so far 

 as they are instanced in Alaska. 



Apparently no records have lieen ])ul)]ished concerning the 

 effect of migTation on the parasites of fishes with the exception 

 of those given Ijy Zschokke and others who have worked iipon 

 the migrations of the European salmon. Tlu' results Zschokke 

 obtained are presented in tliree jiapers (ISSl). 1891, 1902) and 

 give a most comprehensive review of conditions in the case of 

 the Atlantic species as observed on the shores of Europe. If T 

 may be jjermitted to follow somewhat closely his account, the 

 case stands as follows : 



Richly hiden with parasites the Khine salmon, Salmo salar, 

 enters upon its journey in fresh water. In the course of its wan- 

 derings it loses more and more these parasites which inhabit the 

 open intestines below the pyloric coeca ; and since it fasts while 

 ascending the Rhine, and thus the door for the invasion of para- 

 sitic worms is closed, it secures no fresli sujjply. Even thus the 

 salmon at Basel afi'ords an unusually rich booty of parasites, 

 harl)oring more than twice as many s])ecies as any fresh water 

 fish at that place. There still remain in the fish the inhabitants 

 of the anterior ])art of the alimentarv canal and those which can 

 retire there so that ])arasites which in other hosts inhabit only 

 the intestine, occur in the stomach and oesophagus of the Rhine 



