^ 10 



s 



number of Parasites Occurlng In Fillets Exanined 



Figure 4. "Frequency distribution of porosites in misc. 

 rockfish (excluHing S. alutus) from middle area. 



Southern Area 



Fish taken in three trips, all landed 

 in the Astoria area, were sampled. 

 From 60,000 pounds of Pacific ocean 

 perch landed, 37 5 fillets were exam- 

 ined. The data obtained are shown in 

 table 1 and figure 3. 



No other species from this area were 

 available for exannination. The general 

 opinion was, however, that 5. .itelanops 

 usually is infested heavily. This fish 

 was also held in disfavor because of its 

 allegedly poor holding characteristics. 



The troublesome parasitic copepods 

 observed in Pacific ocean perch from 

 the northern area were encountered 

 also in fish from the southern area. 

 According to filleters questioned about 

 this parasite, it only occasionally ap- 

 pears in numbers in fish on the line. 

 This sporadic appearance might indi- 

 cate either a cyclic periodicity in oc- 

 currence or localization in certain 

 grounds fished only occasionally. In- 

 sufficient information is available to 

 say which, if either, of these explana- 

 tions is correct. 



An odd condition that might be mis- 

 taken for parasitization was encoun- 



tered in some of the Pacific ocean 

 perch fronri the southern area. It took 

 the fornn of so-called "blemishes," 

 resembling a kernel of unpolished rice 

 in size and appearance and occurring 

 in the muscle. These blemishes have 

 been examined by Mr. J. Uzmann of 

 the United States Fish and Wildlife 

 Service and have tentatively been iden- 

 tified as aberrant cartilaginous tissue. 

 They have caused trouble with pur- 

 chases made under Federal specifica- 

 tions in the past, but now are officially 

 recognized by the purchasing authori- 

 ties as "harnnless and edible." 



DISCUSSION 



Geographic Distribution 



The incidence of parasitization of 

 perch was high in the northern area. 

 In this survey, 39 percent of the Pacific 

 ocean perch were infested, but reliable 

 informants assert that in many land- 

 ings, the percentage infested is even 

 higher, up to 90 percent of the catch. 



It is interesting to note thateven with- 

 in the Northern area the extent of 

 parasite infestation seenned to vary. 

 Thus the most northerly catch exam- 

 ined, from Hecate Strait, showed an 

 average of nearly seven parasites per 

 infested fillet (table 5). Nevertheless, 

 the percentage of fish parasitized was 

 similar in this sample and in other 

 samples from the Northern area (see 

 table 6 and discussion below). More 

 than 50 percent of the infested fish 

 contained only one or tv/o parasites 

 per fillet (table 3), but nnore than 20 

 percent contained more than five per 

 fillet. The part of the fillet nnost com- 

 monly parasitized was the tail portion, 

 but there was a high incidence of para- 

 sites in the thick, nneaty "shoulder" 

 portion of the fillet (area A, table 2). 



The incidence of parasitism in ocean 

 perch caught in the middle area was 

 about one -half that observed in the 

 northern area, though it was still high. 

 Tv,^o-thirds of the infested fillets con- 

 tained only two or fewer parasites per 

 fillet. Less than 10 percent showed 

 more than five parasites per fillet, 

 and none sho\ved more than nine per 



