Geographic Differences in the Number of Longitudinal Scales of the Ayu Plecoglossus altivelis

Geographic Differences in the Numberof Longitudinal Scales of the Ayu Plecoglossus altivelis Mutsumi Nishida* and Yasumasa Sawashi* (Accepted December 1, 1986) The ayu Plecoglossus altivelis of the Japan and Ryukyu Islands were recently found to differ considerably in both morphological and biochemical-genetic characters, and, within the Japan lslands region, a landlocked population of Lake Biwa to bear traits somewhat different from those of other amphidromous populations.1,2)Azuma3) showed a large difference in the number of longitudinal scales in two samples of Lake Biwa and amghidromous populations, but so far, this particular aspect has not been investigated in much detail.In the present study, investigation was made of geogaphic variation in this number using the same samples from various localities in the Japan and Ryukyu Islands as those in the previous study.2)The following 7 population samples were examined (the sample codes were the same as in the previous study2)): 3) Yoshida River, Miyagi Pref., 43 inds.; 5A) Ado River, Lake Biwa system, Shiga Pref., 31; 8) Nita River, Tsushima Is., Nagasaki Pref., 30; 10) Chunji River, Cheju Is., Korea, 14; 12B) Amori River, Kagoshima Pref., 32; 14B) Sumiyo River, Amamioshima Is., the Ryukyus, Kagoshima Pref., 25; 15B) Yona River, Okinawa Is., the Ryukyus, Okinawa Pref., 31.The longitudinal row of scales dorsal to those on the lateral line were counted, starting with the most posterior scale touching the shoulder girdle and proceeding to the end of the hypural plate, according to the method of Hubbs and Lagler.4)Specimens were weakly stained with cyanine when counted.