Oyster farming is a commercial activity for which medium to high concentrations of nutrients and phytoplankton are required, in order to satisfy the nutritional needs of the farmed organisms and to produce commercially attractive products. These conditions are rarely met in the Ligurian Sea (Italy), that is characterized by oligotrophic conditions. To overcome this limit, a novel IMTA-based approach was adopted by AQUA srl, which involves farming of filter feeders downstream from finfish cages. The research was conducted with the academic support of the University of Genoa. Both organizations are partners in the IDREEM project.
Integrated multi-trophic aquaculture: growing oysters downstream fish cages
In the experimental set-up tested at AQUA farms, lanterns containing Ostrea edulis and Crassostrea gigas were placed downstream from the finfish cages, in order to receive the particulate matter falling off the cages. Lanterns were placed at 7 and 14 m depth to test for an effect of depth in allowing for a higher feed availability and growth. This experiment lasted from June 2013 to May 2014. Shell length, whole wet weight, percent of soft parts and mortality were monitored in November 2013 and May 2014.
Both oyster species reached a legal size for commercialization (60 mm according to the Italian law) during the 12 months farming trial. Their weight placed them both in the medium commercial size class 3 (66-85 g), which sales at a market price of around 9.60 € for O. edulis and 2.50 € for C. gigas.
Besides demonstrating that oysters can be farmed in the oligotrophic Ligurian Sea, these results provide encouraging evidence that they can be profitably grown to a commercial size by using an integrated multi-trophic aquaculture farming model. Furthermore, this IMTA model offers a potential effective solution for reducing the environmental impact of farm effluents.