374 
Fishery Bulletin 99(2) 
\ Gulf of Alaska 
Comparative parasite prevalence 
B 
Gulf of Alaska 
Comparative parasite intensity 
Southern Northern 
rock sole rock sole 
Southern Northern 
rock sole rock sole 
Northern rock sole 
Comparative parasite prevalence 
40 
Aleutian Islands Gulf of Alaska 
Aleutian Islands Gulf of Alaska 
Figure 2 
(A) Prevalence of Naobranchia occidentalis and Nectobrachia indivisa on northern and southern rock sole in the 
Gulf of Alaska. (B) Mean intensity of parasite infestation on northern and southern rock sole in the Gulf of Alaska. 
(C) Prevalence of Naobranchia occidentalis and Nectobrachia indivisa on northern rock sole in the Gulf of Alaska 
and Aleutian Islands. (D) Mean intensity of parasite infestation on northern rock sole in the Gulf of Alaska and 
Aleutian Islands. 
postreproduetive adult Naobranchia occidentalis was found 
in the Gulf of Alaska samples. The original at-sea identifica- 
tion of the two rock sole species was confirmed for all but 
one fish in the laboratory (a northern rock sole was incor- 
rectly identified at sea as a southern rock sole). 
Both Naobranchia occidentalis and Nectobrachia indivi- 
sa were more prevalent (chi square test, a=0.05, P<0.001) 
on the northern rock sole (22% and 15%' of the 225 
fish examined, respectively) than on the southern rock 
sole (5% and 1% of the 282 fish examined, respectively, 
Fig. 2A). Mean intensity was not significantly different be- 
tween the northern (4.4/fish, range 1-22) and southern 
rock sole (2.9/fish, range 1-13) for Naobranchia occiden- 
talis (Welch’s approximate t-test, a=0.05, df=28, P=0.08, 
Fig. 2B) owing to a single southern rock sole with 13 
parasites. Mean intensity also was not significantly differ- 
ent between the northern and the southern rock sole for 
Nectobrachia indivisa (Welch’s approximate f-test, a=0.05, 
df=2, P>0.05); however only two southern rock soles were 
infested with N. indivisa. A chi-square test showed that 
infestation of northern rock sole by N. indivisa was not 
independent of infestation by Naobranchia occidentalis 
(a=0.05, PcO.OOl). Thus, northern rock sole infested by 
one species of parasite had an increased likelihood of also 
being infested by the other. However, infestation of south- 
ern rock sole by Nectobrachia indivisa was independent of 
infestation by Naobranchia occidentalis (P> 0.05). 
Aleutian Islands Only northern rock soles were identified 
at sea in sampled hauls from the Aleutian Islands region, 
and laboratory analysis confirmed their species identifica- 
tion. A total of 237 northern rock soles from 8 trawl hauls 
was examined at sea for gill parasites: 90 fish appeared to 
have at least one gill parasite and their heads were frozen 
