Distribution of the topmouth gudgeon (Pseudorasbora parva) in the Okhotsk region, Hokkaido

Abstract

Topmouth gudgeon (Pseudorasbora parva; Japanese name, motsugo), originally distributed in western Honshu, Shikoku and Kyushu, has been artificially introduced well north of its natural distribution area, to the Tohoku region and Hokkaido. The occurrence of topmouth gudgeon in the pond of Notsukeushi park at Kitami City, Hokkaido, the first record of the species in the Okhotsk region, was established and the population size estimated using the mark-recapture method. Although more than 2,000 fish between 1 and 4 years old were determined as living in the pond, none were found in either the inflow and outflow rivers, despite their apparent suitability. Further efforts in public educations are required to prevent further spreading of this fish.