Table 2. — Parasitic infestation of Pacific ocean perch 



Corrected value for unskinned fillets. 

 ^ Value obtained by dividing column 6 by column 3. 

 sites per fish, multiply by 2. 



For the mean number of para- 



regarding the relationship between 

 parasitization and geographic location. 

 More fish are parasitized, and more 

 fish have a large number of parasites 

 per fish in the northern area than in 

 the middle area, euid in the middle 

 area than in the southern area. Higher 

 levels of infestation were observed 

 this year than in 1958 (45 percent, 44 

 percent, and 27 percent, respectively. 



Table 3. — Percentage incidence of 



parasitization of Pacific ocean perch 

 according to fishing ground 



for the northern, middle, and southern 

 areas in 1959 as compared with 39 

 percent, 21 percent, and 15 percent 

 for the corresponding areas in 1958). 

 Although it is possible that this dif- 

 ference was due to seasonal effects, 

 since this year's investigation was 

 carried out in late spring and last 

 year's in summer, other factors -- 

 such as the migratory habits of the 

 fish, the year class of fish sampled, 

 environmental effects, abundance of 

 the intermediate host, and so on-- 

 could have caused the increase. 



Prosorhynchus was the most com- 

 monly observed parasite, infesting 

 some 39.4 percent of the fillets ex- 

 anciined. Porracaecutn decipiens was 

 encountered rarely, in only 0.001 per- 

 cent of the fillets. This finding, similar 

 to that made last year, confirms that 

 the trematode Prosorhynchus presents 

 the major commercial parasite prob- 

 lem in rockfish of the Pacific North- 

 west area. 



No further light has been shed by 

 this second survey on the reasons for 



