Current status and early life history of amphidromous ayu Plecoglossus altivelis altivelis were studied on Yakushima Island, southern Japan. Although the subspecies had been previously confirmed as distributed in five rivers on the island (Nagata, Isso, Miyanoura, Anbo, and Kurio Rivers), environmental DNA analysis strongly suggested that the population densities were generally low, and that the Anbo River population had disappeared. Spawning of the population in the Kurio River, the southern distribution limit of the subspecies in Japan, occurred in November, primarily around mid-month. Individuals reached 21.3 mm body length 35 days after hatching, the main food items being calanoid copepods. Upstream migrating individuals were observed in early April, suggesting that they remained in estuarine and marine waters for almost four months.
