琵琶湖の南湖へ流入する都市小河川へのビワマスの遡上記録

抄録

A fish specimen [ca. 39 cm standard length (SL)] collected on 11 November 2022 in the Azuma River (a small urban river feeding the South Basin of Lake Biwa) was identified as Biwa salmon (Oncorhynchus masou subsp.), based on morphology and DNA analysis of the mitochondrial ATPase6 and CO III genes. Although the specimen when collected was in very poor condition, lacking several vertebrae and internal organs (including the gonads), the jaw shape, nuptial color on the body, and white abraded caudal peduncle surface indicated that it was a mature female that had attempted to dig a spawning bed. The river-run specimen represents the first specimen-based record of the subspecies in a river flowing into the South Basin of Lake Biwa, and the southernmost river-run record.