Many species of freshwater fishes and mussels have experienced serious declines, both in terms of their spatial distributions as well as their population sizes. Captive breeding in aquaculture facilities can be an important rescue tool to bridge critical life stages such as insufficient reproduction in the wild, and it can help to increase populations above minimum viable population sizes by stocking of captive-bred animals. Currently, several aquaculture facilities throughout Europe actively contribute to the captive breeding of endangered freshwater fishes and mussels which then become released into the wild.
This contribution addresses the question of how such captive breeding programmes related to conservation of endangered freshwater fishes and mussels can be most effective. Using the examples of the endangered Danube salmon (Hucho hucho), the freshwater pearl mussel (Margaritifera margaritifera) and the European nase (Chondrostoma nasus), the usefulness of genetic monitoring in such programmes will be highlighted. This includes the deduction of guidelines for the informed choice of source populations and parents based on genetic pre-screening, and the consideration of selection, genetic drift and adaptation to certain environmental conditions during the breeding and rearing process. The examples will also be used to illustrate possible pitfalls such as inbreeding and outbreeding effects as well as measures to avoid such effects.
The three presented case studies show that conservation-oriented captive breeding in aquaculture facilities need to be managed different to classical food-production oriented aquaculture systems, e.g. in terms of origin and numbers of spawners, their sex ratios and exchange rates. Rearing conditions need to mimic natural habitat and avoid selection of features that are disadvantageous in the wild. The findings also suggest that, depending on the differences in life histories of the species, multiple production cycles and long-terms programmes can reduce the risk of deleterious genetic effects. In many cases, populations of freshwater fishes and mussels would go extinct in the nearby future without captive breeding and stocking actions taken. In addition, juveniles available from such programmes provide a valuable source for ecotoxicological testings and bioindication experiments.