Pfiesteria shumwayae Kills Fish by Micropredation not Ecotoxin Secretion

Anecdotal evidence suggested that Pfiesteria piscicida and P. shumwayae secrete strong exotoxins that led to fish lesion episodes, acute fish kills, and human disease in the estuaries of the mid-Atlantic US. Researchers utilized three different methodologies to evaluate the mechanisms by which P. shumwayae kills fish. Findings from larval fish bioassays indicated that mortility events happened only in cases where fish and dinospores were in physical contact. No evidence of mortalities was found for treatments where a membrane prohibited contact between dinospores and fish. Analyses based on video-micrography and electron microscopy showed dinospores swarming toward and attaching to skin, actively feeding, and rapidly denuding fish of epidermis.