Host Species for Glochidia of the Freshwater Unionid Mussel Inversiunio jokohamensis

Abstract

The host species for the glochidia of the freshwater unionid mussel Inversiunio jokohamensis were identified by determining whether these glochidia had infected the following fish taxa collected from a paddy field ditch in Tochigi Prefecture, Kanto area, central Japan: Nipponocypris spp., Gnathopogon elongatus, Carassius spp., Misgurnus anguillicaudatus, Cobitis biwae, Lefua echigonia, and Rhinogobius sp. OR (orange type). The fishes were kept in tanks for 10 or 11 days, and the numbers of glochidia and metamorphosed juveniles detached from the hosts were counted. Living juveniles detached from the bodies of only Nipponocypris spp., L. echigonia, and Rhinogobius sp. OR. The number of glochidia infecting the fishes, the infection site, and the rate of glochidial encystment were determined using formalin-fixed specimens of N. temminckii, N. sieboldii, G. elongatus, Ca. buergeri subsp.1, M. anguillicaudatus, Co. biwae, L. echigonia, Rhinogobius sp. OR, and the frog Hyla japonica (tadpole). Glochidia had infected 3 host species i.e. L. echigonia, Rhinogobius sp. OR, and N. temminckii. Most glochidia were attached to the gills and fins of the fishes. More glochidia were attached to and encysted on L. echigonia and Rhinogobius sp. OR than on N. temminckii. L. echigonia was identified as a new host species for the glochidia of I. jokohamensis in addition to Rhinogobius sp. OR and N. temminckii.