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<br />140
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<br />
<br />Infestation of SOCkeye Salmon, Oncorhynchus nerka,
<br />
<br />with the Plerocercoids of Diphyllobothrium sp,
<br />
<br />in the Kamchatka River Basin
<br />
<br />V.F. Bugaev
<br />
<br />Kamchatka Branch, Pacific Fisheries and Oceanography Research Institute
<br />KoTINRO Petropavlovsk-Ka~chatskiy
<br />
<br />'Infestation of spawners of 26 local populations and juvenile
<br />sockeye salmon, Onaorhynahus nerka, from 16 rearing ponds in the
<br />Kamchatka River basin, with the plerocercoids of Diphyllobothrium
<br />sp, was studied, On the basis of extent of infestation the river
<br />populations were divided into healthy, mildly infested (5-25%), and
<br />strongly infested (65-75%) groups. Analysis of the year to year
<br />differences confirms the~xistence of groups proposed on the basis
<br />of extent of infestation. ' The intensity of infestation of sockeye
<br />spawners, on an average, varies from 1.29 to 3.26 plerocercoids,
<br />The associations between extent and intensity of infestation with
<br />sex and scale structure were examined. The causes of differential
<br />infestation of individual populations and groups are discussed.
<br />
<br />\-
<br />One'of the largest populations of sockeye salmon, Oncorhynchus nerka, in Asia
<br />occurs in the Kamchatka River, This population forms local secondary subpopula-
<br />tions in different parts of the river basin with a total area of about 56,000 km2,
<br />Differentiation of these subpopulations has a great theoretical and economic sig-
<br />nificance,
<br />
<br />Konovalov (1971) identified a part of sockeye population from the Kamchatka
<br />River in the sea on the basis of infestation with plerocercoids of Diphyllobothrium
<br />sp, and scale structure. Later studies on sockeye salmon from Lake Azabach'e con-
<br />firmed the utility of studies on ecological peculiarities of the ,freshwater period
<br />of life (Konovalov et al., 1971; Konovalov. 1972. 1974. 1980). We used this well-
<br />tested method to locate Kamchatka sockeye during reproduction period (Bugaev, 1978).
<br />Presently, the infestation of sockeye salmon with the plerocercoids of Diphyl-
<br />lobothrium sp,within the entire Kamchatka basin has been studied.
<br />
<br />METHODS
<br />
<br />Infestation of spawners of 26 local populations (Fig. 1) and juvenile sockeye
<br />$almon from 16 rearing ponds (Table 1) in the Kamchatka basin was studied during
<br />i975-1979, A total of 4105 spawners and 1400 young were fixed in formalin for
<br />~tudy, In addition, information was obtained on the infestation of sockeye spawners
<br />from Lake Azabach'e which were collected in the previous years by the scientists of
<br />the Institute of Marine Biology Far East Research Center, USSR Academy of Sciences
<br />(Valdivostok),
<br />
<br />All plerocercoids observed are of type II (according to Konovalov, 1971) and
<br />are similar to the plerocercoid of type "B" (of Petrushevskiy, 1940). There is a
<br />cyst with a thin translucent membrane, which contains 1, rarely 2-3, plerocercoids.
<br />The cysts are located at the junction of abdomen and intestine, and they are poorly
<br />or not at all attached, The plerocercoids start moving actively after opening of
<br />
<br />141
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