The endangered pearl mussel (Margaritifera margaritifera) and thick mullet (Unio crassus) are reared at the Kalborn mill shellfish farm. The aim of this work is to reintroduce the mussels into the river as soon as they have reached a size where they are no longer buried, but can be seen in the riverbed. This increases their probability of survival. Until the mussels can be released back into the wild, various measures are taken to improve the quality of our waterways as habitat. These measures benefit not only mussels, but all other aquatic organisms.
Mussel rearing is highly complex: first, mussel larvae are collected after being ejected by adult mussels to infest host fish. The small mussels, less than half a millimetre in size, which develop on the host fish, are captured in special nets, then reared in plastic boxes in a temperature-controlled cabinet, where they are fed single-cell algae. The mussels grow very slowly; after around four years, they have reached a maximum of two to three centimetres. The first experiments in large crates with gravel have already been carried out.