As a part of our studies on the mechanism of uptake of paralytic shellfish poison (PSP) and the kinetics of its accumulation in bivalves, oysters Crassostrea gigas were experimentally contaminated with PSP by being fed with the toxic dinoflagellate Alexandrium tamarense for 2, 4, 6, 8 and 10 days. Temporal variations in the PSP contents and their profiles in oysters during the feeding experiment were monitored by high-performance liquid chromatography (HPLC) and the toxin profile of the oysters was compared with that of A. tamarense. Toxins excreted from the infested oysters into the seawater for 2 and 10 days were recovered and analyzed by HPLC. PSP toxicity rapidly appeared in the tissues of oysters and their toxicity levels reached 0.6 (0.3), 2.2 (1.1), 1.0 (0.5), 3.4 (1.6) and 1.1 (0.5) MU/g (nmol/g) shucked meat at 2, 4, 6, 8 and 10 days, respectively. The accumulation rates of toxin, calculated from the total amount (nmol) of toxins expressed by the total cell number fed during the exposure period and the toxicity of the oysters, were 14.1, 18.7, 5.1, 14.9 and 3.2῍ for 2, 4, 6, 8 and 10 days. During feeding experiments, the toxin profile of oysters changed substantially, showing marked di#erences from the proportions found in the toxigenic dinoflagellate used as food. The toxin components in this strain existed almost exclusively as b-epimers, which accounted for 66.3 mol῍ of the total. This contrasts with the case of the oysters, where the b-epimers represented 24. 8, 29.8, 25.1, 27.3 and 25.2 mol῍ of the total at 2, 4, 6, 8 and 10 days, respectively. The amount of gonyautoxin-1 (GTX1) accumulated in oysters increased linearly and slowly for 8 days and the maximum content of GTX1 reached 51.3 mol῍. The composition of GTX group compounds recovered from the seawater in which the oysters had been reared was a little di#erent from that within the oyster tissues.

As a part of our studies on paralytic shellfish poison (PSP) accumulation kinetics in bivalves, short-necked clam Tapes japonia was experimentally contaminated with PSP by being fed with the toxic dinoflagellate Alexandrium tamarense for 2, 4, 6, 8 and 10 days, and the processes of PSP accumulation and bioconversion were investigated: the toxicity level was determined by mouse bioassay and toxin components were identified by high-performance liquid chromatography (HPLC). The strain of A. tamarense used in this study possessed a specific toxicity of 186.7῍81 (mean῍S.D., n῏5)῎10ῌ6 MU/cell. Total toxin concentration of this strain was 140.4῍61 (mean῍ S.D., n῏5) fmol/cell. The toxicity level of short-necked clams increased almost in parallel with the abundance of A. tamarense, reaching 1.8, 3.2, 3.8, 3.5 and 4.6 MU/g meat for 2, 4, 6, 8 and 10 days of feeding, respectively. The accumulation rates of PSP toxins, which are the ratio of the total amount of toxins accumulated in the bivalves to the estimated intake in each feeding experiment, were 7.5, 8.1, 5.7, 4.2 and 4.4ῌ for 2, 4, 6, 8 and 10 days, respectively. At the end of each exposure period, many undigested algal cells were found in pseudofeces under microscopic observation. There was a remarkable di#erence in the relative proportions of the predominant toxin components between A. tamarense and short-necked clams. The most notable di#erence was the change in the relative amounts of C2 (carbamoyl-N-sulfo-11 b-hydroxysaxitoxin sulfate), GTX1 and GTX 4 during the first two days. In the toxic bivalves, the amount of C2, which is dominant in A. tamarense, decreased to below half a percent after being ingested. Subsequently, the amount of GTX1 in the shellfish meat reached 50.1 molῌ, while that of GTX4 decreased to about half of that in A. tamarense. As for the configuration of 11-hydroxysulfate, PSP components in A. tamarense exist almost exclusively as b-epimers (GTX3, GTX4, C2 and C4), accounting for 72.8 molῌ of the total. This contrasts with the case of the short-necked clams, where the b-epimers represented 25. 8, 33.8, 30.8, 36.8 and 28.5 molῌ of the total after 2, 4, 6, 8 and 10 days, respectively. PSP components seemed to be converted rapidly at an early stage of the feeding of A. tamarense.