The endangered thick-shelled river mussel (Unio crassus): a new host species for the European bitterling (Rhodeus amarus)

Krzysztof Tatoj,Katarzyna Zając,Tadeusz Zając,Adam M Ćmiel,Anna M Lipińska,Dorota Kwaśna

doi:10.1007/s10531-017-1295-y

Krzysztof Tatoj, Katarzyna Zając + Show 4 more

Open Access

https://doi.org/10.1007/s10531-017-1295-y

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Abstract

Large freshwater mussels (Unionoida) are declining throughout the world. The European bitterling Rhodeus amarus (Bloch, 1782) female spawns its eggs inside the unionids’ shells, where fertilisation and further embryonic development take place; thus its reproduction depends fully on the presence of large freshwater mussels. Unio crassus, previously regarded as one of the most numerous unionids in Europe, is now listed in the IUCN Red Data List as being globally endangered. Despite its previous prevalence, it was never reported as a host for the bitterling. A large population of U. crassus was studied in small river at the Świętokrzyskie Mts (Poland), where also electrofishing was conducted. In each bitterling territory located on the study plots, we found individuals of U. crassus, with the bitterling eggs or larvae developing on mussel’s gills. That proves that this species can be also used by the bitterling for reproduction. We suggest that this relationship has not been reported to date due to the mussels’ rarity and ongoing decline. However, it is also possible that the endangered mussel is a novel host for the bitterling, which is expanding its range throughout Europe.

Highlights

The European bitterling Rhodeus amarus (Bloch, 1782) is a small cyprinid fish with a unique life cycle, characterised by an obligatory relationship with freshwater mussels
The mussel species used by R. amarus for spawning in the western part of its geographical range appear to be hosts with a short evolutionary association with this fish species (Reichard et al 2006)
The species seems to have been relatively abundant in the downstream parts of such lowland rivers as the Rhine, Meuse, and Schelde from about the eleventh century to the start of severe aquatic pollution in the nineteenth century (Wolff 1968)

Summary

Introduction

The European bitterling Rhodeus amarus (Bloch, 1782) is a small cyprinid fish with a unique life cycle, characterised by an obligatory relationship with freshwater mussels. The bitterling female spawns its eggs between the gills of unionid mussels, where fertilisation. This article belongs to the Topical Collection: Invasive species. Biodivers Conserv (2017) 26:1217–1224 and further embryonic development takes place (Aldridge 1999). Due to its unique mode of reproduction, the occurrence of the European bitterling is limited and depends on the presence of unionids (Przybylski and Zieba 2000). In Europe, the bitterling is mostly regarded as rare and endangered (Lelek 1987; Przybylski 2002)

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