376 
Fishery Bulletin 99(2) 
Figure 3 
Length frequency of male and female northern rock sole examined for parasites from the Gulf of Alaska. Numbers of 
fish infested with one parasite species added to those infested with the other parasite species may exceed the total 
because several fish were infested with both parasite species. 
a preference for middle gill arches, and overall, there was 
a slight preference for outer arches (Table 3). Although 
there were numerous juvenile Naobranchia occidentalis 
parasites on northern rock soles from the Aleutian Is- 
lands, their individual positions were not recorded sepa- 
rately from the adults. 
Trends in parasite infestations— species, sex, and size 
Gulf of Alaska A wide size range of northern rock sole 
males (15-42 cm FL) and females (14-54 cm FL) were 
examined for parasites during the Gulf of Alaska survey 
(Fig. 3), but Naobranchia occidentalis was found only on 
larger males (28-40 cm FL) and females (29-51 cm FL). 
Similarly, Nectobrachia indivisa was found only on larger 
males (28-40 cm FL) and females (29-51 cm FL), with the 
exception of a single, small (21 cm FL) infested female. 
None of the male southern rock soles (19-40 cm FL) 
were infested with either parasite species, but male south- 
ern rock soles were uncommon in our survey catches and 
only 28 fish were examined (Fig. 4). A total of 254 female 
southern rock soles ( 14-58 cm FL) were examined for par- 
asites during the survey and Naobranchia occidentalis in- 
fested only 14 of the larger females (42-52 cm FL). Only 
two relatively large (37 and 47 cm FL) female southern 
rock soles were infested with Nectobrachia indivisa. 
Aleutian Islands Male (19-37 cm FL) and female (20-46 
cm FL) northern rock soles from the Aleutian Islands were 
examined, and Naobranchia occidentalis was found only 
in larger individuals (24-37 cm FL males and 28-44 cm 
FL females, Fig. 5). The size range of fish infested with 
Nectobrachia indivisa was slightly more restricted (24-33 
cm FL males and 28-43 cm FL females) than the size 
range of fish infested with Naobranchia occidentalis. 
Length-weight relationships 
Parasitized (range 28-40 cm FL) and unparasitized (range 
18-36 cm FL) male northern rock soles from the Gulf of 
