We investigated the occurrence of unionid bivalves during the non-irrigation season of 2013 at 132 locations in two agricultural channels in Kawajima Town, Saitama Prefecture, where a small number of the alien species Lanceolaria grayana(Lea, 1834)was first found in 2005. We found a total of 255 individuals at 56 locations widely distributed throughout the channels. Generalized linear models revealed that the density of L. grayana depends mostly on water depth and to a lesser extent on substrate type, but not on substrate compaction, current velocity, vegetation cover ratio, electrical conductivity, or dissolved oxygen. We found three native unionid species(Pronodularia japanensis, Unio douglasiae nipponensis, and Anodonta sp.), densities of which were much lower than that of L. grayana. Further studies are needed to address to what extent L. grayana has spread to surrounding areas and its impact on native unionid species.
The host species for the glochidia of the freshwater unionid mussels, Hyriopsis schlegeli, Inversiunio jokohamensis and Sinanodonta spp. were identified by determining whether these glochidia had infected the following fish taxa collected from Lake Anenuma in Aomori Prefecture, Tohoku area, Japan: Carassius cuvieri, Carassius sp., Acheilognathus melanogaster, Rhodeus ocellatus ocellatus, Tribolodon hakonensis, Pseudorasbora parva, Misgurnus anguillicaudatus, Silurus asotus, Hypomesus nipponensis, Pungitius sp. 1, Tridentiger brevispinis, Rhinogobius spp. and Gymnogobius castaneus. The fishes were kept in tanks for 2-8 days, and the numbers of glochidia and metamorphosed juveniles detached from the hosts were counted. Living juveniles of H. schlegeli detached from the bodies of S. asotus, Trid. brevispinis, and G. castaneus. Living juveniles of I. jokohamensis detached from the bodies of Trib. hakonensis, Trid. brevispinis, and G. castaneus. Living juveniles of Sinanodonta spp. detached from the bodies of only G. castaneus. These fishes were identified as suitable new host species for the glochidia of H. schlegeli, I. jokohamensis and Sinanodonta spp. in Lake Anenuma.