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olivaceus against the monogenean Neoheterobothrium hirame were identified. With electron microscopy, peripheral blood leucocytes (PBL) of Japanese flounder could be classified into four types: lymphocytes, thrombocytes, monocytes and granulocytes.Granulocytes were positive for acid phosphatase and peroxidase activities, and stained with Sudan black B. In fish infected with N. hirame, the ratios of granulocytes and monocytes significantly increased in the PBL composition.Infiltration of monocytes/macrophages and granulocytes, and cells having large electron-dense granules (DGC) was observed in the infection sites. These cells were often ob served adhering to the tegument of N. hirame. Monocytes/macrophages showed particularly higher adherent ability to N. hirame than the other leucocytes under in vitro and in vivo conditions. We conclude that monocytes/macrophages, granulocytes and DGC are major effector cells in the defense of the flounder against N. hirame.

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Sakhalin taimen Hucho perryi populations have decreased drastically to near extinction. It is urgent to establish an effective conservation strategy based on an understanding of the characteristics of migration and habitat use of this species. We examined the migration history of anadromous Sakhalin taimen captured off the Sarufutsu coast, northern Hokkaido, Japan, using otolith Sr:Ca ratios and also examined the relationship between their otolith Sr:Ca ratios during freshwater and seawater residence in a rearing experiment. Otolith Sr:Ca ratios of some fish from the Sarufutsu coast showed freshwater levels (0.5-4.0 9 10 -3 ) near the core, which thereafter increased to brackish water levels (4.0-6.0 9 10 -3 ), and then to seawater levels (6.0-10.0 9 10 -3 ) in the outermost regions. Those findings indicate that specimens from the Sarufutsu coast migrated to the brackish water region or the sea and spent most of their lives there. The anadromous migration pattern including the timing of downstream migration seems to be flexible among individuals in the species. They migrate between freshwater and seawater or brackish water several times during their lives, showing extensive habitat use. It is essential to secure the continuity among the freshwater, brackish water, and seawater areas for their effective conservation.