Three species of bivalves (mussel, hard clam, and surf clam) were collected in 1990-98 in Ibaraki Prefecture, Japan, and assayed for toxicity and composition of paralytic shellfish poison (PSP). All the species of bivalves were found to be toxic every or every other year; they became toxic in March or early April and nontoxic in May. Their digestive glands showed the highest toxicity scores, ranging from 100 to 300MU/g. Irrespective of the species and parts (“muscle” and “visceral” parts), PSP was composed almost exclusively of protogonyautoxins (PXs) 1, 2 and gonyautoxins (GTXs) 1-4. The PSP composition profile, however, was species-specific and differed between the two parts in each species. The ratio of N1-OH toxins (GTX1, GTX4) to N1-H toxins (GTX2, GTX3) differed significantly among the species. The ratio also differed between the two parts of both clams, though not in the mussel. This suggested that species- and organ-specific metabolism could have taken place in the viscera.
In each species, on the other hand, the ratio of α-epimer (GTX1) to β-epimer (GTX4) at position C11 tended to increase up to the equilibrium point of 3:1.