Spawning of Gnathopogon caerulescens, Carassius buergeri grandoculis, and Japanese Cyprinus species in a revetmented tributary of the Chounogi River flowing into Lake Biwa, as revealed by DNA identification of field-collected eggs

Abstract

A total of 351 eggs from 12 egg populations was collected in June 2018 from a revetmented tributary of the Chounogi River, ca. 2 km upstream from Lake Biwa. Analysis of 95 of these eggs (sampled about equally from all populations) by a 2 or 3-step DNA identification process resulted in 71 being successfully sorted into the following five taxa: Gnathopogon caerulescens (25 eggs), Carassius buergeri grandoculis (22), triploid Carassius (4), and Japanese (8) and Eurasian (12) species of Cyprinus. Of these five taxa, G. caerulescens, C. buergeri grandoculis, and Japanese Cyprinus sp. are thought to migrate upstream to spawn, as they are more commonly found in the lake. Notably, 60% of the collected eggs were attached to the substrata provided by riverside trees (the remaining 40% were attached to vegetation hanging into the stream). Unfortunately, these trees were removed during a river renovation procedure conducted just after this study.