Coloured scanning electron micrograph (SEM) of toxic heterotrophic dinoflagellate, Pfiesteria piscidica. Pfiesteria has been associated with harmful algal blooms (toxic bloom, red tide), fish kills and causing health problems in humans. It differs from most known toxin producing algae in that it does not produce a pigment and thus gives no visual evidence of its activity. A complex life cycle of Pfiesteria complex organisms (PCOs) has been claimed to be responsible for large fish kills in the 1980s and 1990s on the East Coast of the USA. Pfiesteria biology and the role of PCOs in killing fish and causing health issues in humans have been subject to controversies and conflicting research results. Researchers have isolated and characterized the toxin of Pfiesteria piscidica as a metal complex and free radical toxin. They have also identified how the dinoflagellate transforms from a non-toxic to toxic state. Magnification: x2,135 when shortest axis.
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