Comparison of hemolytic activities among strains of Heterocapsa circularisquama isolated in various localities in Japan.

Heterocapsa circularisquama (Dinophyceae), a red tide dinoflagellate, is toxic to bivalve molluscs such as the pearl oyster (Pinctada fucata), but no harmful effects of this alga on fish have been observed so far. We found that 7 strains of H. circularisquama showed hemolytic activities toward rabbit erythrocytes in a cell-density dependent manner, but to quite different extents. The strains which are known to be highly toxic to bivalves tend to show stronger hemolytic activities and vice versa, suggesting that the hemolytic activity is parallel with the shellfish toxicity of H. circularisquama. Since the hemolytic assay is simple, semiquantitative, and reproducible, this assay is useful not only to search for certain toxins responsible for the shellfish toxicity of H. circularisquama but also to estimate the potential toxicity of a newly appeared strain of H. circularisquama.