-The objective of this study was to identify a possible effect of food on the acceleration of decontamination in blue mussels, Mytilus edulis, containing diarrhetic toxins belonging to the okadaic acid (OA) structural group. An experimental protocol was designed to describe and compare the decontamination kinetics and detoxification rates of naturally OA-contaminated mussels that had either received or not received food for three weeks. The protocol was applied in two trials (in June 2006 and June 2007, called Ker06 and Ker07), conducted one year apart on samples of mussels collected in the same area, at the same season. Okadaic acid (OA), the main lipophilic toxin produced by the toxic alga Dinophysis acuminata, was analysed over the course of the decontamination, in hydrolysed (total OA) and non hydrolysed (free OA) digestive gland extracts, in order to estimate acyl-esters (7-O-acyl-ester derivatives of OA) concentrations. OA analyses were also made for toxin presence in biodeposits and in the aqueous phase. Bivalve physiological status was evaluated by biomass measurements (dry weight of flesh) and two biochemical compounds (total lipid and glycogen concentrations). Measured physiological parameters showed that mussels did not suffer under experimental conditions. Both trials showed that the food accelerated the elimination of free and total OA. This effect cannot be attributed to a dilution of the toxin in the tissue, as results expressed in toxin burden led to the same conclusion. The kinetic models of decontamination differed between the two experiments: the model was linear for Ker06, provided that the values corresponding to the first two days were discarded, whereas data fitted a decreasing exponential curve better in Ker07. Detoxification rates increased as the food supply increased. After three weeks of experimentation, the detoxification rates for total OA in Ker06 and Ker07 were 52 and 61%, respectively, in unfed mussels and 90 and 89% in fed mussels (with the highest level in Ker07). Comparisons between the free OA and esters showed that detoxification rate was higher for free OA than for esters, whatever the level of food supply. The results of this study suggest that food increase probably accelerates elimination of OA and OA-esters but the latter are eliminated at a lower speed. Key words:Mussel / Feeding / Digestive gland / Depuration / Okadaic acid / Acyl esters / Marine lipophilic biotoxins / Mass spectrometry Résumé -L'objectif de cette étude est de mettre en évidence un effet éventuel de la nourriture sur la vitesse de décontamination de moules, Mytilus edulis, contenant des toxines diarrhéiques de la famille de l'acide okadaïque (OA). Un protocole expérimental est conçu pour décrire les cinétiques durant 3 semaines d'expérience et comparer les taux de détoxication d'une part chez des moules nourries et d'autre part chez des moules maintenues à jeun. Ce protocole est appliqué sur des moules prélevées au même endroit, à la même saison, en 2006et 2007. L'acide okadaïque, principale ...

International audienceIn response to the closure of shellfish production sites due to increasing occurrence of toxic algal blooms, land-based recirculating aquaculture systems (RAS) could be used by producers to store a proportion of their stock temporarily. An RAS prototype was tested in this study to store Pacific oyster Crassostrea gigas over a range of temperatures. In such systems, the water temperature is a variable that could influence the bivalve excretion rate of ammonia, the concentration of which may become critical for the water quality. In this study, we first estimated the total ammonia nitrogen (TAN, N-NH4+ + N-NH3) excretion of the Pacific oyster and then investigated whether the bacterial population associated with the oysters could act as a natural biofilter by measuring the potential nitrification rate (PNR) of the shell. The TAN excretion rate varied significantly with temperature. The PNRs were significantly different depending on the shell surface considered with a PNR of 0.42 ± 0.11 (SD) nmol N cm−2 h−1 for the internal part, 0.96 ± 0.15 (SD) nmol N cm−2 h−1 for the external part of the shell. In addition, a 5-week experiment was conducted with a 180 kg of oyster stock stored in a 1900 L RAS to monitor TAN concentration and to establish a TAN budget at the level of an oyster population. The TAN concentration sharply declined in the RAS after 6 days and a stable concentration of 3.3 ± 0.91 (SD) μmol N L−1 was reached till the end of the experiment. This measurement, as well as the estimation of a theoretical TAN budget based on the previous experiments, showed that the PNR and some other associated processes were sufficient to counteract the ammonia fluxes excreted by the oysters. This result underlines the significant role played by the nitrifying bacterial population colonizing the bivalve shell and suggests that such an oyster stock could be stored in a recirculating tank without the addition of a biofilter, which would represent a real economic advantage

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