Décontamination expérimentale de bivalves toxiques : application aux phycotoxines paralysantes. Rapport final

A sea water recirculating flume was especially designed in the framework of this study. It improves physiological and ecophysiological evaluation of a 25 oysters (c. gigas) set fed on PSP toxic A. minutum cultures and then detoxified with commonly used aquaculture species (I. galbana, T. suecica, S. costatum, T. weissflogii). Chlorophyll a levels are kept steady in each case and adjusted in order to reach the same food value in each tank (0,5 mg/l TPM). When exposed to the mildly toxic species A. minutum (0,5 pg.eq.STX.cel-1) oysters depict a reduced clearance rate, food uptake and shell-valves activity (compared to non-toxic algal diets). The same physiological parameters do not show any significant differences when oysters are exposed to the control al gal diet, i.e the non-toxic dinoflagellate S. trochoidea. Decreased shell-valve activity with A. minutum (only 50 % oyster actively clearing) do not prevent toxin accumulation in oyster tissues within 15 days, up to max. level of 300 µg.eq.STX.100 g-1. The following 15 d depuration period rapidly (4 days) makes B toxins levels falling down below the 80 µg.eq.STX.100 g-1 sanitary threshold, whatever algal diet used, but with a higher depuration efficiency with 1 galbana, which displays higher proportions of lipids. No significant difference in biochemical composition is observed in oysters at the end of depuration phase, whatever microalgal diet is considered. Elevated individual variations of toxin content by oyster cannot be properly understood without considering the individual mean shell-valve activy during contamination period.