Early research suggested a very complex life cycle of Pfiesteria piscicida with up to 24 different stages, spanning from cyst to several amoeboid forms with toxic zoospores.

[2] However these results have become controversial as additional research has found only a simple haplontic life cycle with no toxic amoeboid stages[3] and amoebae present on attacked fish may represent an unrelated species of protist.

At a multi-state workshop at the Centers for Disease Control and Prevention (CDC) in Atlanta, U.S., at the end of September 1997, attendees agreed on clinical symptoms that characterize a new illness associated with Pfiesteria exposure.

These clinical features include: With these criteria and environmental qualifiers (e.g., 22% of a 50-fish sample, all of the same species, have lesions caused by a toxin), it is likely that Pfiesteria-related surveillance data can better track potential illnesses.

Duke University Medical Center researchers conducted experiments on rats, which showed that the toxin appeared to slow learning but did not affect memory.