Accidental arks: conserving monopisthocotylan parasite species through European weatherfish captive breeding

Abstract

Most ex-situ conservation programs ignore parasites or entail their active removal from host individuals. This can cause the decline or even the extinction of parasite species. However, alternative scenarios are possible. We present a case study in which three potentially endangered parasite species may be conserved as a byproduct of the host ex-situ conservation program. The European weatherfish (Misgurnus fossilis, Cobitidae) is a freshwater fish critically endangered in Belgium, threatened by habitat loss, pollution and invasion by two Asian congeners. Regional conservation actions of this species in Belgium include a captive breeding and re-introduction program. We assessed infection of these captive weatherfish and characterized (both morphologically and genetically) their ectoparasites. Three species of Monopisthocotyla were found: Actinocleidus cruciatus (Dactylogyridea) and Gyrodactylus misgurni (Gyrodactylidea) on the gills, G. fossilis (Gyrodactylidea) on the skin. Two of these parasites were also observed in historical weatherfish specimens originally collected in Belgium between 1932-1973, before the invasion of exotic weatherfishes, indicating that these parasites are native to the country. All three monopisthocotylan species were previously suggested to be threatened by extinction in the Czech Republic and Slovakia. Wild historical and captive fish had similar infection abundances, but they differed in their infection parameters. DNA barcoding of these parasites provided new markers, until now lacking, that can be used for detecting these conservation-relevant parasites in nature. The ex-situ breeding conditions of captive breeding stock of European weatherfish offers the possibility to sustain both the host population and populations of at least two parasite species, at abundance levels that are not harmful for the host. Thus, the captive breeding program of the European weatherfish is also relevant for preserving its parasites, without allocating additional resources. Discussion among stakeholders about a policy with regard to parasite conservation is needed. We advocate for conservation efforts going beyond hosts and integrating native host-parasite combinations (as a package entity) in ex-situ breeding and re-introductions in nature.