Abstract
Host preference in Margaritifera laevis was investigated via field and laboratory studies on two populations in the Shinano River System. Although there was no difference in the growth curve of glochidia during the parasitic period, or in the size of the resulting juvenile mussels, the host species were different. The masu trout (Oncorhynchus masou masou) was the host in the Chubu-Nogu River but not in the Sakasa River, whereas the whitespotted char (Salvelinus leucomaenis) was the host in the Sakasa River but not in the Chubu-Nogu River. This difference in host species suggests that there may be two Margaritifera species in Japan.
