Abstract
Japanese surf smelt, Hypomesus pretiosus japonicus, from 8 localities in Hokkaido and 7 localities in the Tohoku district, olive rainbow smelt, Osmerus eperlanus mordax, from 2 localities in Hokkaido, and Japanese smelt, H. transpacificus nipponensis from 7 localities in Honshu and 2 localities in Hokkaido in Japan were examined for plerocercoids of the family Diphyllobothriidae. Plerocercoids were found in Japanese surf smelt in all of the 15 localities in which they were surveyed. The prevalence of plerocercoids ranged from 4.4 to 31.3% (average 25.0%) in fish from Hokkaido and from 10.0% to 83.6% (average 49.3%) in fish from the Tohoku district. We also noted that the prevalence of plerocercoids increase as the length of the fish increased, with marked increase in fish of body length of 8, 11, and 13 cm. Plerocercoids were also found in olive rainbow smelt in both of the localities in which they were surveyed. The prevalence of plerocercoids was 5.5% in the fish taken from the coast of Muroran and 51.3% in those taken from Lagoon Notoro in Hokkaido. No plerocercoids were found in Japanese smelt. All of the plerocercoids were found in the abdominal cavity of the infected fish; the intensity of plerocercoids per fish ranged from 1 to 15 (total average 2.13). We found very few morphometric or histologic differences between the results of our studies of plerocercoids, including adult worms reared in golden hamsters and cestode eggs, and those of Yazaki et al., (1988). Therefore, we identified this tapeworm as Diphyllobothorium hottai.
Key words: Diphyllobothorium hottai; osmerid fish; plerocercoid; prevalence; morphology.

Correspondence:Akihiko Uchida

Yoshihiko Murata
Yasushi Kawakami
Hideka Kimura
Akihiko Uchida
Department of Environmental Biology, College of Environmental Health, Azabu University, Sagamihara, Kanagawa 229, Japan.