A population of freshwater Ayu (Plecoglossus altivelis altivelis) was found in the “wandos”, semi-enclosed remnants of artificial pond-like structures along the Yodo River at Shirokita, upstream of the Yodo River barrage. Microsatellite analysis of collected individuals showed their genetic origin to be a Lake Biwa strain, with a hatching date between September and November, estimated by otolith analysis. Otolith strontium and calcium concentrations indicated no history of seaward migration, the individuals analyzed having inhabited freshwater since hatching. In addition, eDNA analysis suggested that they had migrated from the main river course into the “wandos” in November.
