Oceanian-type black rat (Rattus rattus) found in Port Otaru of Hokkaido, Japan

Abstract

Karyological survey showed that the Oceanian-type black rat (Rattus rattus; chromosome number 2n=38) was distributed in Otaru, Hokkaido, Japan. All of 18 rats trapped in Port Otaru in 1999 and 2000 were this type, whereas 78 other rats collected in other ports of Japan were Asian type (Rattus rattus; 2n=42/41). The Oceanian-type population in Otaru is suggested to have originated from rats that had recently escaped from foreign vessels that called at the port. This is the first record of the Oceanian-type black rat in the mainland of Japan.