Abstract
The most characteristic difference of Japanese Diphyllobothrium latum from those of European and Canadian species is it's second intermediate host. The Japanese Diphyllobothrium latum take genus Oncorhynchus as it's most important 2nd intermediate host and plerocercoids are always found in their fillet not in their viscera which phenomena can not be observed in the cases of the latter Diphyllobothrium.
From 1977 to 1982, we examined 723 Cherry salmon, Oncorhynchus masou which were caught in the northern Japan Sea from March to May every year. Out of 723 Cherry salmon, 218 (30.2%) were showed the infection of plerocercoids of D. latum (Table 1 & 2). The yearly data of the infection rate of fish varied from 15.9 to 48.4%. The plerocercoids were found most likely in the back hind part of the fish (Figure 1).
The sex ratios (Table 4) of Cherry salmon caught in the Japan Sea indicated that thesr sal mon was mainly derivled not from Japanese rivers, but from Kamchatka, Sakhalin or the coastal part of Siverian continent (Table 3.)
It remains totally unknown where these Cherry salmon got infection of D. latum.
