II72 



BULI.ETIN OF THE BUREAU OF FISHERIES. 



PARASITES OF PACIFIC SALMON. 



The list of parasites for Atlantic salmon in America, though small, is much 

 more extended than the records concerning the Pacific salmon. While tremen- 

 dous numbers of the latter fish, which belong to several species of the genus Onco- 

 rhynchus, are taken every year for commercial purposes, apparently no one has 

 studied the parasitic fauna or done more than to record casually a few data 

 taken during a study of some other factor concerning the species. Even of such 

 notes I have found only a very few. 



In a report on the life history of the Alaska salmon, Bean (1890, and also 

 1893) noted a few items concerning parasites. He mentions the presence in 

 1889 of numerous intestinal worms in the red salmon and finds that all species of 

 salmon [in fresh water?] are more or less covered with parasitic copepoda. 



Much more extensive are the notes made by the brilliant young naturalist 

 and student of the Pacific salmon, Cloudsley Rutter, who only a short time 

 back met such an untimely death. 



In the course of investigations on the natural history of the quinnat salmon 

 in the Sacramento River, Rutter (1902) records some interesting items regarding 

 their parasites. A common pest in the adult of this species in fresh water is a 

 parasitic copepod which attaches itself to the gill filaments. Usually not 

 numerous on a single fish, they yet sometimes destroy the gill filaments almost 

 entirely. The intestine of the spawning salmon is frequentl)' inhabited by 

 tapeworms extending into the coeca and at times filling them completely. They 

 do not occur in the stomach. In 1898 they were much more abundant than in 

 1900. Among 200 young salmon examined from fresh-water stations in the 

 Sacramento basin in May, 1898, and April, 1899, parasites were found in the 

 stomach contents of 3 1 fish. They were described as of two or three kinds, one 

 elongated [cestode?], the others short and grain-like [trematodes?]. Rutter 

 thinks that residence in fresh water is conducive to the growth of parasites in 

 the stomachs of young salmon. He gives the following tables of their occurrence 

 according to size of host and dates of capture. 



Occurrence of Parasites in Quinnat Salmon from Sacramento River. 

 According to dales of capture. 



