We describe several reproductive characteristics of two types of Japanese charr Salvelinus leucomaenis found in Arimine Lake, an artificial lake-inlet stream system in Toyama, Japan. Larger-sized individuals, which migrate downstream to the lake and grow to maturity there, later migrate up several inlet streams to spawn. Smaller-sized individuals, however, are resident in streams and spawn there. These types are respectively similar to sea-run or lake-run and stream resident types of other salmonid fish. During the 26 years following lake construction by damming, the migratory life cycle of part of the population of this charr appears to have changed from the fluvial form. During spawning activity, mature females and males presumably form pairs of each type, with the pair formation assortatively depending upon their body size.