Captive breeding of the endangered freshwater pearl mussel Margaritifera margaritifera

Freshwater pearl mussels (Unionidae: Bivalvia) rank among the most endangered aquatic invertebrates, and this has recently prompted a number of initiatives designed to propagate the species through captive breeding. Yet there are few guidelines to aid in freshwater mussel culture for conservation, and few or no results on the fate of released juveniles. We reviewed various ex situ strategies for freshwater mussel conservation with emphasis on the freshwater pearl mussel Margaritifera margaritifera (L.), one of the most critically endangered unionids. Captive breeding could help safeguard critically endangered populations, but current rearing methods need to be optimised. Areas in particular need of research include the collection and storage of viable glochidia, the development of efficient rearing systems, and the formulation of algal diets. Likewise, the degree of host specificity warrants further investigation, as this will largely dictate the success of reintroduction programmes. Finally, we note that more information is needed on the degree of genetic structuring and post-release survival before translocation programmes can be recommended. As with other conservation projects, captive breeding of the freshwater pearl mussel cannot compensate for loss of critical habitats and is likely to be most efficient in combination with in situ conservation, not in isolation.