Direct impact of invasive bivalve (<Emphasis Type="Italic">Sinanodonta woodiana</Emphasis>) parasitism on freshwater fish physiology: evidence and implications

Direct and potentially damaging effects of invasive alien species can remain unnoticed or insufficiently quantified, resulting in a lack of stakeholder awareness. We report for the first time that parasitic larvae (glochidia) of the invasive freshwater mussel Sinanodonta (Anodonta) woodiana (Unionidae, Bivalvia) cause an unexpected reduction in the condition factor of parasitized native fish species. The reduction in the body mass and condition factor of experimentally infested European chub (Squalius cephalus) was associated with changes in several physiological parameters measured in host fish plasma. Ion concentrations (potassium, chloride) and enzymes activities (aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, alkaline phosphatase) were significantly affected; hence, the results reveal the complex effects of non-native glochidia on the homeostasis of the individually tested fish. Changes in host physiology and condition status were recorded also in environmentally relevant infestation intensities (mean of 3.02 ± 0.51 glochidia g^?1). Despite intensive concern regarding the negative biodiversity and ecosystem impacts of the adult stage of S. woodiana among conservationists and natural resource managers, potential effects of its larval stage have been neglected until now. Because fish hosts are an obligatory part of the reproductive cycle of the mussel and the main vector for spreading, documentation of this direct and easily quantifiable impact on fish has great potential to influence the key community of stakeholders in fisheries and aquaculture sectors and to serve as a strong motivating factor for invasive species control. We argue for more careful consideration of potential multiple life-stage effects of S. woodiana and of other invasive alien species as well, as different life stages can have highly specific impacts and corresponding relevance for key stakeholder groups.