SOME POINTS IN THE MIGRATION OF PACIFIC 



SALMON AS SHOWN BY ITS 



PARASITES 



BY HENEY B. WAKD. OF THE UXIVEHSITY OF NEBRASKA. 



The Pacific salmon nianifosts some strange features in its 

 lii'e liistorv which are of sncli interest as to call for whatever evi- 

 dence can he secured to establish their precise character. Two 

 years ago through the courtes}- of C^'ommissioner G-eorge M. Bow- 

 el's of the Bureau of Fisheries, I had the opportunity of spend- 

 ing a sunnner in Alaska investigating the parasites of the sal- 

 mon. My sincere thanks are due thi' l)ureau and Commissioner 

 Powers for this unique opportunity to study a most interesting 

 subject. While the large amount of material collected there has 

 not been ]nit in final condition for tlu' complete report and in any 

 event would l)e rather too extensive to warrant re])eating it here, 

 yet tliere are certain results of such general interest that they 

 may properly be presented on an occasion of this type. This is 

 all the more true since they east a most interesting light on the 

 com])arative biology of the Atlantic and Pacific salmon. 



It is possible to gather from the parasitic fauna of any ani- 

 mal clear evidence of its habits. Even though the knowledge be 

 incomplete one may demonstrate some of the changes through 

 which the animal has passed. In fact the parasites of any ani- 

 mal will show elearly the range of its dispersal, the period of 

 (l('velo])nient it has I'eacbed, the character of its food material, 

 and the tyi)e of medium in which it lives. Whatever changes, 

 \isual or e.\ce])tional. are expei-ienccd during its career leave a 

 record of their character in the list of its parasites. 



To illustrate this it is only necessary to cite one or two in- 

 teresting examples in order to place clearly before your minds 

 the general principle I have just stated. In 1899 Linton found 

 that eels caught in the sea harbor ])arasites which are primarily 

 marine in origin and secondarily of fresh water type. Even 

 more striking is the observation of Zschokke (1902) in his stu- 

 dies on the lawyer (Lota vulgaris), which is the only fresh wa- 

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