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.

蚌目（Unionida）贻贝的钩介幼虫（glochidia）需与宿主鱼类形成专性共生关系，方能完成自身生命周期。为探明受威胁的新西兰埃基齿蚌（Echyridella aucklandica）此前未被发现的宿主鱼类关联，研究人员在怀卡托地区的四条溪流中，定量测定了两种贻贝对鱼类的钩介幼虫感染情况。研究首次确定了E. aucklandica的宿主：钩介幼虫可附着并形成胞囊于普通胡瓜鱼（Retropinna retropinna）的鳃部，而未在其他捕获的鱼类物种上检出感染。与之形成鲜明对比的是，门氏埃基齿蚌（E. menziesii）可在多种鱼类物种上寄生，却未在捕获的两尾R. retropinna个体上发现感染迹象。包囊于宿主体内的E. aucklandica钩介幼虫展现出在宿主鱼类鳃部生长的实证。本初步研究结果为新西兰同域分布的蚌目贻贝物种与其钩介幼虫的共生互作机制提供了关键认知，可为兼顾蚌目群落与宿主鱼类种群的整合式保护管理工作提供重要支撑。