Optimisation of the traditional Pacific cupped oyster (Crassostrea gigas Thunberg) culture on the French Atlantic coastline: autumnal fattening in semi-closed ponds

Oyster farming in France is a traditional activity. Each year, 60,000 tons of C. gigas are fattened before being sold. Present-day fattening technique s for improving oyster taste and colour and increasing the meat weight are not particularly reliable. To optimize the fattening process, large phytopl anktonic blooms were induced in ponds, then distributed in oyster ponds. De spite the variability of the autumn weather conditions, diatoms (Skeletonem a costatum) have been successfully cultured in outdoor ponds. During neap t ides (when no seawater replenishes the water in the oyster beds), between m id-October and mid-December 1996, the fattening index (the weight of the me at) was constant or increased by 10-15% when a supplement of algae of 380.0 00 cells/oyster/day was added to the ponds. Algal supplement was clearly re sponsible for fattening improvement. In 1995, the addition of 110,000 cells /oyster/day, a significantly lower quantity, was not sufficient to prevent weight loss. Over two periods of 3 months (in 1995 and 1996) of the experim ent, a significant reduction in weight (up to 20%) was observed in oysters grown in ponds which did not receive additional algae. (C) 2001 Elsevier Sc ience B.V. All rights reserved.