Table 6 — Statistical analysis of percentage infestation data 



Fishing area Mean percent Standard Upper limit of Lower limit of 



fish parasitize** deviation parasitization«* parasitizatiowt* 



* Mean • weighted according to total hailed catch. 

 »» Established at 95 percent confidence level; that is, ± 2 x S.D. 



In view of the importance of parasiti- 

 zatlon in relation to Federal purchases, 

 the industry tries to ensure that all 

 Pacific ocean perch landed in the area 

 are equally free from parasites. The 

 buyers often refuse to purchase fish 

 caught in the heavily parasitized Hecate 

 Strait area. 



Table 3 summarizes the results for 

 the three areas and shows clearly that 

 both the incidence and the degree of 

 parasitization decrease from north to 

 south. It should be remembered, how- 

 ever, that this investigation was con- 

 ducted only during the summer. Further 

 investigations are necessary to estab- 

 lish whether seasonal factors may in- 

 fluence the geographical distribution. 



Two theories are available to accovint 

 for the observations. According to one 

 theory, the extent of parasitization is 

 dependent primarily upon the size of 

 the host-fish population. When large 

 populations exist, many hosts are avail- 

 able, and parasitization is high. As 

 was indicated above, this theory is in 

 accord with what is known about the 

 abundance of Pacific ocean perch in the 

 three areas considered. If the theory is 

 correct, then intensive, controlled fish- 

 ing of the northern areas would seem 

 to be the only practical method of re- 

 ducing parasitization. 



The second theory is dependent on the 

 fact that a Prosorhynchus sp. is the prin- 

 cipal parasite infesting Pacific ocean 



perch and suggests that there is a 

 geographic limit on this parasite or on 

 one of its hosts other than Pacific 

 ocean perch, which amounts to the same 

 thing. Again, this theory seems to be 

 equally possible. 



The economic intiportance of the 

 problenn would indicate the advisability 

 of a study to determine which, if either, 

 of these two theories is correct. 



Distribution of Parasites in the Fillets 



The distribution of the parasites in 

 the fillets is shown in table 2. If only 

 S. alutus, which is the species given the 

 most study, is considered, the areas 

 showing the greatest infestation ranged 

 in the order C. A, F, B, E, D, with 

 area C showing the most infestation and 

 area D, the least. Thus the greatest 

 amount of infestation was in the tail 

 and the shoulder portions of the fillets. 



It is fortunate that most parasites 

 occur in the tail portion, since the 

 nnusculature is thin in the tail of the 

 fish, and the whole area can be cut off 

 the fillet without much loss. In some 

 plants, the trimming is more or less 

 automatically done during skinning. 



The parasitization of the "shoulder" 

 region is much more difficult to deal 

 with, since this is the most meaty 

 portion of the fish. Individual cutting 

 out of the parasites in this area is 



