TAIL 



Lolerol line 



Figure 2. --Division of the fillet into arbitrary areas for 

 parasite count. 



plant we worked markets his product. 

 Inasmuch as the skin interferes with 

 the detection of parasites, a correction 

 factor had to be applied to the data 

 found with these unskinned fillets. 



Since unskinned fillets were not avail- 

 able at the time set aside for the de- 

 termination of the correction factor, 

 skinned fillets taken at random from a 

 fillet line were used instead. In deter- 

 mining the factor, we candled each 

 fillet from the bone side and noted the 

 presence or absence of parasites; the 

 fillet then was turned over and was 

 candled fronn the skin side for the 

 detection of any parasites not previ- 

 ously discovered, which gave the data 

 needed to calculate the correction fac- 

 tor: 



No. fronn both sides 

 No. bone side 



RESULTS AND DISCUSSION 



blemishes differ somewhat, these two 

 topics are conveniently considered un- 

 der separate headings. 



Parasites 



Correction factor . --The data ob- 

 tained in the evaluation of the correction 

 factor are given in table 1. The factor 

 described here is conservative, since 

 the removal of the skin permits some- 

 what better transmission of light 

 through the fillet than is possible when 

 the skin is present and thus aids in the 

 detection of parasites from the bone 

 side. In short, the correction factor 

 does not overly correct. 



Geographical distribution . --Data on 

 parasitic infestation of Pacific ocean 

 perch according to fishing area, by 

 individual trip, are given in table 2. 

 Summarizing data are given in table 3. 

 Weighted mean values and range of 

 variability in parasitic infestation from 

 catch to catch are given in table 4. 

 The weighted mean values for percent 

 infestation shown in table 4, which take 

 into account the weight of fish in each 

 of the catches sampled, differ little 

 from the calculated means shown in 

 table 3. The standard deviations (table 

 4) of the weighted mean parasitization 

 was greatest this year for the nothern 

 area. Last year it was greatest for 

 the middle and southern areas. 



Since the results obtained in the 

 study of the parasites and that of the 



In general, the results of the present 

 survey confirm our previous findings 



Table 1. — Correction factor 



r, .J « 4. (No. from both sides) 217 _ , ^^ 



Correction factor = ^■-; r^ = z-^;^ " 1-20 



No. bone side 180 



