Discovery of a host fish species for the threatened New Zealand freshwater mussel Echyridella aucklandica (Bivalvia: Unionida: Hyriidae)

Larvae (glochidia) of Unionida mussels form obligate symbiotic associations with host fish to complete their life-cycle. To identify previously unknown host fish associations for the threatened New Zealand Echyridella aucklandica, glochidia infestation on fish by two mussel species was quantified in four Waikato streams. A host for E. aucklandica was identified for the first time, with glochidia found to attach and encyst on the common smelt Retropinna retropinna but not on other fish species caught. In contrast, E. menziesii was found on a range of fish species but not on the two R. retropinna caught. Encysted E. aucklandica glochidia showed evidence of growth on the gills of host fish. These preliminary results provide critical knowledge of host–glochidia interactions in sympatric New Zealand unionid species to support integrated conservation management targeting both unionid communities and host fish populations.