Differential parasitism by Naobranchia occidentalis (Copepoda : Naobranchiidae) and Nectobrachia indivisa (Copepoda : Lernaeopodidae) on northern rock sole (Lepidopsetta polyxystra Orr and Matarese, 2000) and southern rock sole (L-bilineata Ayres, 1855) in Alaskan waters

Northern rock sole (Lepidopsetta polyxystra Orr and Matarese, 2000) and sou thern rock sole it. bilineata Ayres, 1855) from the Gulf of Alaska and nort hern rock sole from the Aleutian Islands were examined for gill parasites. Four species of copepod parasites were identified: Naobranchia occidentalis and Nectobrachia indivisa were the most common. Both parasites were more p revalent on northern lock sole (22% and 15%, respectively) than on southern rock sole (5% and 1%, respectively) in the Gulf of Alaska samples. Norther n rock sole tended to have a greater mean intensity of Naobranchia occident alis than southern rock sole but there was not a significant difference bec ause of the high variance about the means; too few southern rock sole were infested by Nectobrachia indivisa for comparison. Northern rock sole from t he Aleutian Islands region had a significantly greater prevalence (36%) and mean intensity (10.2/infested fish) of Naobranchia occidentalis than north ern rock sole from the Gulf of Alaska (22%, and 4.4, respectively) but did not differ significantly in prevalence and mean intensity of Nectobrachia i ndivisa. Parasitized male northern rock sole from the Gulf of Alaska had a significantly reduced weight at length, indicating a possible Effect of par asitism. Naobranchia occidentalis selectively infested larger northern rock sole and only the largest southern rock sole. Nectobrachia indivisa also w ere found on larger northern rock sole but did not infest enough southern r ock sole to describe a trend. Southern rock sole males were not infested by either parasite. Naobranchia occidentalis preferred to infest the middle g ill arches of hosts and Nectobrachia indivisa preferred to infest the exter ior gill arches of hosts.