Optimizing laboratory cultures of Gammarus fossarum (Crustacea: Amphipoda) as a study organism in environmental sciences and ecotoxicology

Amphipods are among the most abundant macroinvertebrates in freshwater ecosystems of the Palaearctic and crucial for ecosystem functioning. Furthermore, their high sensitivity to environmental change and pollutants makes them widely used model organisms in environmental sciences and ecotoxicology. In field studies and surveys across Eurasia, species of the genus Gammarus are commonly used, yet laboratory-based studies and ecotoxicological tests are often restricted to the inmost parts of the world non-native Hyalella azteca, as Gammarus is much harder to breed and maintain under laboratory conditions. However, for direct comparisons and extrapolations of results of field- vs. laboratory-based studies, the use of the same species would be desirable. Here, we investigated different settings with respect to feeding, shelter and day length to successfully increase survival, juvenile production and their respective growth and survival, and ultimately multi-generation breeding of the amphipod Gammarus fossarum. Amphipod populations persisted and reproduced successfully under optimized husbandry conditions for 12 months and were partially maintained for another year in populations up to a few hundred individuals. Specifically, supplementing diet with protein-rich food sources as well as the provisioning of shelters improved survival rate of G. fossarum significantly. However, we found no significant effect of different day length treatments on the overall relative reproductive activity or on the total amphipod abundancemaintained. We conclude that G. fossarum can be kept and reared under standardized conditions. Despite the longer generation times of G. fossarum and higher effort required for maintenance compared to H. azteca, direct ecological relevance and comparability of results to natural systemsmay justify its future use and development as a study organism for environmental sciences and ecotoxicology.