Significant amounts of paralybc shellfish toxins (PSP toxins) were detected in particles in the slze fraction 0.45 to 5 pm in seawater from Ofunato Bay, Japan, collected at a time when the toxicity of scallop increased in the absence of the causative organism Protogonyaulax tarnarensis. Toxin in the same fraction was negligible when scallop toxicity was decreasing. PSP toxins were also detected in the bacterial fraction from cell-free cultured medium of P. tamarensis. Previously, we reported

more »

... t Moraxella sp. isolated from P. tarnarensis produces PSP toxins. About 17 and 60 '10 respectively of bacteria in the seawater and the cultured medium of P tamarensis reacted with anti-Moraxella sp. serum. These results suggest that PSP toxin-produc~ng bacteria are present in the environn~ental water and are responsible for bivalve toxicity.