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Several experiments using a self-regulated system were conducted to define the factors likely to influence the uptake of paralytic shellfish poison (PSP) by oysters in the Penzé estuary (France, Brittany). Each 4-day experiment was carried out in a recirculated sea water system using 15 Pacific oysters (Crassostrea gigas) separated from each other and supplied with unfiltered natural seawater containing alternatively toxic (Alexandrium minutum) or non-toxic (Skeletonema costatum) algal diets. The food supply and exposure times to toxic diets were determined according to field studies of the upstream and downstream movement of patches containing A. minutum. The experimental parameters corresponded roughly to the hydrological conditions generally observed in June when tidal coefficients are lowest and blooms occur: (i) A. minutum concentrations in sea water of 200, 5000 and 10 000 cell ml$^{-1}$; (ii) inorganic matter consisting of 5 and 15 mg L$^{-1 }$ of calcinated muddy sediments; and (iii) low and high tide salinities of 25 and 35‰, respectively. Significant experimental contamination (greater than the 80 $\mu $g STX equiv. 100 g$^{-1}$ sanitary threshold) occurred after 4 days of exposure for the monospecific A. minutum diet (20-200 cell ml$^{-1})$ and alternated A. minutum and S. costatum diets (5000 and 20 000 cell ml$^{-1}$, respectively). Contamination levels were less than the sanitary threshold for alternated A. minutum/S. costatum diets of 200 and 20 000 cell ml$^{-1}$, respectively, and for a monospecific A. minutum diet (1000-10 000 cell ml$^{-1})$. In the last case, the accumulation rate was quite low, possibly because of inhibition of the filtration rate related to a lower biodeposit production rate and decreased feeding time activity. The addition of inorganic matter appeared to play a significant role in the observed increase of toxin uptake, whereas salinity was not a determining factor for toxin accumulation rates. These last observations were corroborated by statistical analysis and stepwise multiple linear regressions integrating all or some of the experimental parameters.

Several experiments using a self-regulated system were conducted to define the factors likely to influence the uptake of paralytic shellfish poison (PSP) by oysters in the Penzé estuary (France, Brittany). Each 4-day experiment was carried out in a recirculated sea water system using 15 Pacific oysters (Crassostrea gigas) separated from each other and supplied with unfiltered natural seawater containing alternatively toxic (Alexandrium minutum) or non-toxic (Skeletonema costatum) algal diets. The food supply and exposure times to toxic diets were determined according to field studies of the upstream and downstream movement of patches containing A. minutum. The experimental parameters corresponded roughly to the hydrological conditions generally observed in June when tidal coefficients are lowest and blooms occur: (i) A. minutumconcentrations in sea water of 200, 5000 and 10 000 cell ml−1; (ii) inorganic matter consisting of 5 and 15 mg L−1 of calcinated muddy sediments; and (iii) low and high tide salinities of 25 and 35‰, respectively. Significant experimental contamination (greater than the 80 µg STX equiv. 100 g-1sanitary threshold) occurred after 4 days of exposure for the monospecific A. minutum diet (20-200 cell ml−1) and alternated A. minutum and S. costatumdiets (5000 and 20 000 cell ml−1, respectively). Contamination levels were less than the sanitary threshold for alternated A. minutum/S. costatumdiets of 200 and 20 000 cell ml−1, respectively, and for a monospecific A. minutumdiet (1000−10 000 cell ml−1). In the last case, the accumulation rate was quite low, possibly because of inhibition of the filtration rate related to a lower biodeposit production rate and decreased feeding time activity. The addition of inorganic matter appeared to play a significant role in the observed increase of toxin uptake, whereas salinity was not a determining factor for toxin accumulation rates. These last observations were corroborated by statistical analysis and stepwise multiple linear regressions integrating all or some of the experimental parameters.

AbstractThe toxicity of a Prorocentrum limaEhrenberg strain from the French Mediterranean was compared with that of a Spanish strain of the same species. Although the toxic profiles revealed by high-performance liquid chromatography were similar, showing okadaic acid (OA) and dinophysistoxin (DTX1), the French strain contained markedly less toxin. This difference was verified by immunofluorescence techniques for the intracellular localization of OA, which showed sequestration of OA and its derivatives in vacuolar structures on the periphery of the cytoplasm, and these structures appeared to be less concentrated in the French strain at the same culture age. Okadaic acid and its target, protein-phosphatase PP2A, were detected simultaneously by labeling with specific antibodies. The immunolocalization of the protein in a spherical structure close to the centrosomic region was confirmed for both strains. Observations supported the hypothesis that the insensitivity of P. limastrains to OA is due in part to sequestration of the inhibitory substance at a distance (area close to the nucleus) from the target substance, phosphatase, thus preventing their contact.

Since January 1993, neurological symptoms and rapid deaths (5 to 10 min) were typically observed in the mouse bioassay of acetone extracts of digestive glands from Arcachon and Toulon (France) during the winter season. It was assumed initially that a new lipophilic toxin was present because tests using the AOAC mouse bioassay for paralytic shellfish toxins on acid extracts of whole shellfish meat were negative, no known lipophilic toxins were detected and no toxic phytoplankton species were observed in the area during the poisoning events. In this study, however, preparative isolation of the toxic factor from toxic mussel digestive glands has revealed the presence of paralytic shellfish toxins, the principal ones being gonyautoxins-2 and -3 at Arcachon and gonyautoxins-1, -4, -2 and -3 at Toulon. The toxin concentrations recorded were below levels harmful to consumers and therefore represent a false positive in the mouse bioassay for lipophilic toxins based upon acetone extraction. The origin of the toxins remains to be determined. Copyright © 1999 John Wiley & Sons, Ltd.

Since January 1993, neurological symptoms and rapid deaths (5 to 10 min) were typically observed in the mouse bioassay of acetone extracts of digestive glands from Arcachon and Toulon (France) during the winter season. It was assumed initially that a new lipophilic toxin waspresent because tests using the AOAC mouse bioassay for paralytic shellfish toxins on acid extracts of whole shellfish meat were negative, no known lipophilic toxins were detected and no toxic phytoplanktonspecies were observed in the area during the poisoning events. In this study, however, preparative isolation of the toxic factor from toxic mussel digestive glands has revealed the presence of paralytic shellfish toxins, the principal ones being gonyautoxins-2 and -3 at Arcachon and gonyautoxins-1, -4, -2 and -3 at Toulon. The toxin concentrations recorded were below levels harmful to consumers and therefore represent a false positive in the mouse bioassay for lipophilic toxinsbased upon acetone extraction. The origin of the toxins remains to be determined. [ABSTRACT FROM AUTHOR]