What You Should Know About Pfiesteria
Pfiesteria piscicida is a recently discovered, potentially toxic microorganism. It is found naturally in the environment.
Laboratory research indicates Pfiesteria can exist in up to 24 life stages, four of which may be toxic. Like many other dinoflagellate phytoplankton (microscopic algae), Pfiesteria can survive in sediments in a cyst or spore form.
Under specific conditions, such as high nutrient levels and the presence of large schools of fish, Pfiesteria’s population increases. This is referred to as a “bloom.” During a bloom, this organism changes into a free swimming form that may produce toxin(s) which numbs fish and enables Pfiesteria to feed on fish. High levels of toxic Pfiesteria can cause deep, ulcerative lesions on fish, and/or may kill fish. Toxic Pfiesteria blooms typically exist for short periods of time, a few hours to several days.
Many times Pfiesteria may not result in fish kills or lesions. Pfiesteria may spend its entire life feeding harmlessly on bacteria and other algae. It is currently not well understood what environmental factors induce Pfiesteria to produce harmful toxins. In the laboratory, toxic Pfiesteria blooms are induced by the presence of fresh fish.
Pfiesteria has been the cause of several massive fish kills in nutrient-enriched (elevated levels of phosphorus and nitrogen) estuaries along coastal North Carolina. In most of these fish kills, large schools of menhaden were present in warm, shallow, poorly flushed, nutrient enriched estuarine waters.
Exactly how Pfiesteria toxin(s) acts on fish is unknown. Only a few scientists have been studying this organism, so while research is ongoing, little is known definitively about the biology of Pfiesteria or its role in causing fish disease and death.
Pfiesteria in Maryland
A Pfiesteria piscicida-like microorganism was identified in one water sample taken from the lower Pocomoke River in May 1997. Pfiesteria and related organisms were also identified in the Pocomoke during August and in Kings Creek and the Chicamacomico River in September.
The three systems affected by Pfiesteria-like organisms bring to seven the number of systems to contain the organisms in Maryland (other locations include Jenkins Creek in the Choptank watershed; an aquaculture pond off the Manokin watershed; Wye River; and the National Academy of Sciences’ fish tanks on the Patuxent River). It likely exists in many other locations throughout the Chesapeake Bay and Maryland’s coastal bays.
Pfiesteria-like microorganisms have been identified as the most likely cause of the fish kills and the fish lesion events in the Pocomoke and Chicamacomico Rivers and Kings Creek.
A Pfiesteria-like microorganism has not been linked to fish kills in the Chesapeake Bay prior to the August Pocomoke kill.
Fish Health Facts
The temporary closures of portions of three lower Eastern Shore waterways last year due to episodes of toxic Pfiesteria activity resulted in a heightened awareness of fish health among anglers and the general public. For decades, DNR fish biologists have annually examined hundreds of thousands of fish statewide through our various fish and water quality monitoring programs. Additionally, DNR regularly communicates with commercial fishermen, charter boat captains and recreational fishing organizations concerning the health of fish caught in the Chesapeake Bay and its tributaries. Based on this volume of information and experience, DNR offers the following fish health facts and guidance for Maryland anglers:
Maryland fish populations are healthy!
Low levels of abrasions and lesions occur naturally every year in all fish communities.
What is Pfiesteria?
Discovered in 1988 by researchers at North Carolina State University, Pfiesteria piscicida is now known to have a highly complex life-cycle with 24 reported forms, a few of which can produce toxins. Three typical forms are shown on the left. A few other toxic dinoflagellate species with characteristics similar to Pfiesteria have been identified but not yet named. These are referred to as "Pfiesteria-like organisms," and they occur from Delaware to the Gulf of Mexico. (back to the top)
How does Pfiesteria affect fish?
How long do toxic Pfiesteria outbreaks last?
Where has Pfiesteria been found?
Pfiesteria piscicida has been implicated as a cause of major fish kills at many sites along the North Carolina coast, particularly the New River and the Albemarle-Pamlico estuarine system, which includes the Neuse and Tar-Pamlico Rivers. Millions of fish have died from Pfiesteria in North Carolina. In 1997, Pfiesteria or Pfiesteria-like organisms killed thousands of fish in several Eastern Shore tributaries of the Chesapeake Bay, including the Chicamacomico and Manokin Rivers and King's Creek in Maryland, and the lower Pocomoke River in Maryland and Virginia. Pfiesteria piscicida is the probable cause for a 1987 fish kill in Delaware's Indian River. Fish kills in coastal aquaculture operations in Maryland and North Carolina have also been linked to Pfiesteria and Pfiesteria-like organisms. Lesioned fish found in association with Pfiesteria or Pfiesteria-like organisms have been documented in several Maryland and Virginia tributaries of the Chesapeake Bay, in many coastal areas of North Carolina, and in the St. John's River in Florida. (back to the top)
Can Pfiesteria cause human health problems?
Preliminary evidence suggests that exposure to Pfiesteria toxins in the air, water, or fish at the site of an outbreak can cause skin irritation as well as short-term memory loss, confusion, and other cognitive impairments in people. It has been shown that similar human health effects can be caused by exposure to Pfiesteria toxins in a laboratory setting. However, there is no evidence that illnesses related to Pfiesteria are associated with eating fish or shellfish. To date, only Pfiesteria piscicida has been linked to human health problems; other Pfiesteria-like organisms have not been shown to cause human illness.
As of October, 1997, 146 people had reported possible Pfiesteria-related health problems, including researchers working with the toxins in the laboratory, commercial fishermen, a water-skier, and officials working in the field during a fish kill. Symptoms reported by these individuals include skin irritation; memory loss and other cognitive impairments; nausea and vomiting; and respiratory, kidney, liver, vision, and immune system problems. Recent studies suggest that some of these symptoms may be temporary. Establishing a definite link between generalized symptoms and the microbe is difficult, but health officials are studying the situation carefully. (back to the top)
Is it safe to swim and boat in coastal waters?
Is Pfiesteria a harmful algal bloom? How is it related to red and brown tides?
Some kinds of algal blooms are harmful because the algae produce one or more toxins that poison fish or shellfish, and can pose human health risks when people come in contact with affected waters. These toxic algal blooms may also kill seabirds and other animals indirectly as the toxins are passed up the food chain. Certain kinds of these toxic algal blooms can cause human health problems via contaminated seafood, like Ciguatera Fish Poisoning, Amnesic Shellfish Poisoning, and Paralytic Shellfish Poisoning. However, there is no evidence that Pfiesteria-related illnesses are associated with eating fish or shellfish.
Most algal blooms are not toxic, but they are still considered harmful if they reduce the amount of light or oxygen in the water, consequently killing sea grasses, fish or other marine life. Blooms of macroalgae -- seaweed -- can also be harmful if they damage underwater habitats such as coral reefs or sea grass beds. (back to the top)
What causes toxic Pfiesteria outbreaks?
Nutrients such as nitrogen and phosphorus are thought to encourage the growth of Pfiesteria populations by stimulating the growth of algae that Pfiesteria feeds on when in its non-toxic forms. Some evidence suggests that nutrients may also directly stimulate the growth of Pfiesteria, but more research is needed to show this conclusively. At this time, the precise role that nutrients and other factors may play in promoting toxic outbreaks of Pfiesteria is not clear, and is an area of active research.
Excess nutrients are common pollutants in coastal waters. Chief sources of nutrient pollution in coastal areas are sewage treatment plants, septic tanks, polluted runoff from suburban landscapes and agricultural operations, and air pollutants that settle on the land and water. (back to the top)
What is being done about Pfiesteria?
Whom should I contact to report fish lesions, fish kills, or possible human exposure to Pfiesteria?
What is an abrasion?
What is a lesion?
External parasites can also injure fish and may cause lesions. They may be found on gills, fins and skin, sometimes with bleeding at the site of entry.
Most lesions on fish are not associated with Pfiesteria. Lesions that might be associated with Pfiesteria are ulcerative, typically round, dime-sized, deep into the muscle, may be bleeding, and are usually near the anus. Other possible indicators of toxic Pfiesteria:
If you find any of these conditions, please contact the
Fish Health Hotline at 1-877-224-7229.
Is it safe to eat seafood?
To be on the safe side, the following common-sense precautions are recommended:
What should I do if I catch a fish with a serious abnormality?
DNR experts have prepared a technical fish health guide for field biologists, including photos.
For additional information on Pfiesteria and water quality sampling in the Pocomoke River, call the Maryland Department of Natural Resources (DNR) Tidewater Ecosystem Assessment Department at (410) 260-8630. (back to the top)
Is Pfiesteria the only cause of fish lesions and fish kills? Is it possible that previous fish lesion events have been caused by some factor or combination of factors other than Pfiesteria?
During 1997, Maryland experienced four separate events on three rivers that involved fish behaving in an erratic manner, a high proportion of fish with lesions and, in some cases, fish kills. Toxic Pfiesteria was found to be present in high densities at the time and place of all four events. After careful review of these data, the independent Maryland Technical Advisory Committee (TAC) concluded that Pfiesteria was the most probable cause of the fish kills, erratic behavior and lesion initiation. Medical professionals have advised the State that human health threats appear to be associated with these Pfiesteria outbreaks. Medical researchers from the University of Maryland and Johns Hopkins have documented impacts to the health of individuals that had contact with these water bodies in 1997 (recently published in the international, peer-reviewed medical journal, The Lancet). State and outside scientists have known and communicated publicly since the summer of 1997 that fungus and other microbes were found in lesioned fish in the Pfiesteria outbreak areas. Research has shown that fish skin damage caused by Pfiesteria toxins can be followed by the invasion of other microbes that can enlarge the lesion. (back to the top)
Is it appropriate to use the presence of fish with lesions as a reason for closing rivers?
What has Maryland done to evaluate the various hypotheses regarding fish health, Pfiesteria, and its causes?
Is it possible that menhaden found with lesions in tributaries of the Chesapeake Bay have contracted fungal diseases in remote water and then migrated into the Bay?
The State of Maryland assisted in the development of these questions with the following groups:
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