| The North American invasive signal crayfish Pacifastacus leniusculus was designated as an ‘Invasive Alien Species’ by the Ministry of the Environment of Japan and by the Ministry of Agriculture、 Forestry and Fisheries of Japan on 1 February、 2006. We report the first record of P. leniusculus from the Kanto region (Chiba Prefecture)、 central Japan. Adult specimens of P. leniusculus were collected from the Tone River basin between September 2009 and January 2010. Ectosymbiotic crayfish worms (Annelida、 Clitellata、 Branchiobdellidae) were found on the crayfish and all specimens were identified as Sathodrilus attenuatus、 which outside of its home range in North America occurs only in the Hokkaido and Fukushima Prefecture populations of P. leniusculus; thus suggesting that P. leniusculus in the Tone River basin was introduced from Hokkaido or Fukushima Prefecture. Signal crayfish is considered a cool water species and has been reported mostly in Hokkaido、 northern Japan、 but our findings strongly indicate that P. leniusculus has become established in a warm water area in central Japan、 where the maximum water temperature is above 30°C in summer. These results indicate that P. leniusculus can inhabit warm water areas as well as cool areas and would be able to extend its distribution over a wide range in Japan. |
