A floating cage system for freshwater mussels Anodonta anatina and Unio mancus rearing in Piedmont region (NW Italy)

This research represents the first attempt in Italy to develop a cage system for adult freshwater mussel stocking, for extensive farming, that was realized from 2003 to 2005 in NW Italy. Two autochthonous species of Italian freshwater mussel were used: Anodonta anatina and Unio mancus. 5133 mussels were collected and successively stocked in floating cages in 5 different sites in a lake. The experimentation was planned in order to determine the effect of main rearing factors for potential farming: stocking density and cage position in the water column (depth). For each species, the effects of three rearing densities and two water depths were tested. Mussel growth was monthly measured in each experimental unit during all the experimentation. The survival rate at the end of the experimentation for both considered species was 98.4%. U. mancus resulted more resistant to rearing conditions and during the summer the highest mortality was registered for A. anatina. Summer mortality was comprised between 4.8% and 20.5%. Highest mortality of U. mancus was recorded in September 2004 at 1.5 m (3.6 ± 2.4%), while the highest mortality for A. anatina was recorded in September 2003 at 1.5 m of depth, 13.3% ± 3.8%. This research showed that cage stocking is a suitable method and the optimal position of cages is the lake thermocline. The proposed species resulted easily utilizable for future farming or bioremediation projects, resulting readily reared up to 135 kg m-3.