Paralytic Toxins in the Dinoflagellate Gonyaulax excavata and in Shellfish

Paralytic toxins were examined quantitatively in a culture of Gonyaulax excavata and in shellfish by the standard mouse bioassay and by an alkaline peroxide oxidation–fluorometric assay for saxitoxin (STX). The dinoflagellate probably contains at least three toxins, including STX, which represents 3–20% of the total toxin load. During growth in culture the toxin content per cell decreased progressively; however, relative amounts of the three toxins remained roughly similar. In toxic shellfish from nature (Mya arenaria, Mytilus edulis, Modiolus modiolus) and in shellfish fed G. excavata under controlled conditions the relative amounts of toxins differed from those in G. excavata, suggesting toxin interconversions and interference with the chemical assay by toxins other than STX. The consistency in the relationships between bioassay and chemical assay results for clam samples was fair, although the chemical assay measured from 16 to 48% of the bioassay. The chemical assay is questionable as an indicator of total toxin content, and until further data are accumulated the mouse bioassay method is considered more reliable for measuring paralytic, G. excavata toxins in shellfish. Key words: Gonyaulax excavata, dinoflagellate toxins, paralytic shellfish poisoning, saxitoxin, toxin measurement