Attached eggs of Ischikauia steenackeri detected in an inflow channel of the South Basin of Lake Biwa: first recent report from a natural spawning substrate in the Lake Biwa water system

A single egg population sample, G3356 (n = 14), was obtained from fragments of the aquatic plant Myriophyllum spicatum floating on the surface of a small channel flowing into the South Basin of Lake Biwa, Japan, on July 17, 2024. The average egg diameter was 1.47 mm based on image analysis. Five eggs were randomly selected, and the mitochondrial 12S rRNA gene region was partially sequenced (181 bp). All eggs shared a single haplotype and were identified as wataka (Ischikauia steenackeri). These eggs are the first documented evidence of this species utilizing a natural spawning substrate within the Lake Biwa water system in recent years.