Preliminary considerations for freshwater mussel reproduction and possible application for extensive rearing in Italy

The present work is aimed to investigate the physiology of reproduction of freshwater mussel (Anodonta anatina) for future extensive farming. In this paper the knowledge of life history traits and reproductive aspects is considered as the first step for obtaining juveniles for rearing mussels in captivity. In the first part of this research 2,285 specimens of A. anatina were placed in 5 sites in the Avigliana Lakes (NW Italy) and reared for a 2 years period. A sample of 180 specimens was collected in the Lake in November 2003 and 57% of mussels were gravid. The brooding period started from late August to the next spring. Histology performed on 11 individuals collected in April and late June 2004 clearly showed either females or hermaphrodites, confirming that A. anatina sexual strategy is characterised by a high plasticity. In order to obtain juveniles in captivity, a correct assessment of glochidial maturity was necessary. In April hooks of glochidia were completely developed and the adductor muscle was clearly visible. A partial extrusion of the mantle before glochidial release can be considered a good indicator of glochidial maturity, while water temperature and glochidial snapping activity are less reliable. Four Pumpkinseed (Lepomis gibbosus), 8 Bleaks (Alburnus alburnus) and an European Perch (Perca fluviatilis), were infested with glochidia in aquarium, confirming that A. anatina is a low selective host fish species and that host fish parasitism can be easily performed in artificial conditions with fish species commonly found in Avigliana Lakes. A case of direct development to a juvenile A. anatina without the parasitic stage on fish was also observed: a metamorphosed glochidium (juvenile) was found in the genital duct together with sub-triangular glochidia of smaller size. This is the first observation of direct development reported for an European Unionid. Freshwater mussel farming could be interesting activity for the future for bacteria filtration in integrate productions and as alternative feedstuffs for farmed fish nutrition. This preliminary work is the first step for larval rearing and potential future of European freshwater mussel farming.