Relative contribution of exotoxin and micropredation to icthyotoxicity of two strains of Pfiesteria shumwayae (Dinophyceae)

Analysis of variance showed that, for both strains, fish mortality in Pfiesteria-inoculated bioassays was significantly higher than control bioassays both with and without direct contact (P < 0.001). Differences between strains were not significant (P = 0.3). These results indicate that both strains are associated with exotoxin production. However, the dominant and most consistent mechanism of fish mortality observed in this study required physical contact between fish and Pfiesteria cells.