The occurrence and distribution of the threatened nagaremon-charr, a morphotype of Salvelinus leucomaenis japonicus, were investigated in the Ane River system, Lake Biwa basin, Shiga Prefecture, central Japan, in August, 2005. The total numbers of nagaremon-type charr and typical-type charr captured were 20 and 38, respectively. The occurrence of nagaremon-type charr has dropped dramatically compared with the 1970s, suggesting that artificial transplantation might have obscured indigenous gene pools and modified evolutionary distinctions of that morphotype. Nagaremon-type charr were distributed further upstream than the typical-type, a significant only the former being captured above waterfall. These observations suggest that habitat restoration, prohibition of fishing and removal of Salvelinus leucomaenis pluvius are essential for practical conservation of the nagaremon-type charr.
