Pfiesteria, << fees TEER ee uh, >> make up a group of aquatic organisms that can prove harmful to fish, human beings, and other animals. Pfiesteria inhabit coastal regions of eastern North America. They are members of the protist group called dinoflagellates. These are single-celled organisms that typically swim by means of two hairlike structures called flagella. There are two known species of this organism, called Pfiesteria piscicida and P. shumwayae.
Many scientists believe Pfiesteria have a complex life cycle. According to these scientists, most Pfiesteria live buried in sediment in a harmless form called a cyst, but some of them can change into a harmful mobile form when fish swim nearby. It is believed that the mobile forms excrete powerful toxins (poisons) into the water. The toxins weaken the fish, making them swim slowly and enabling disease-causing bacteria and fungi to eat away at their skin. Eventually, the toxins paralyze and kill the fish. Pfiesteria then feed on the dead fish.
Some evidence suggests that human beings and other large animals can be harmed by exposure to water that contains Pfiesteria. People exposed to the organisms may suffer skin sores, nausea, respiratory problems, fatigue, and temporary memory loss.
Pfiesteria were first discovered in 1991 after millions of fish were found killed in waters off North Carolina. Scientists think that pollution, especially fertilizer runoff, sewage, and animal wastes from farms near coastal waters, has caused more frequent Pfiesteria outbreaks.
