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.

Fish Health
ALSO AVAILABLE: Bibliography of Pfiesteria references.


What is Pfiesteria?
three important life stages of Pfiesteria piscicidaPfiesteria piscicida (fee-STEER-ee-uh pis-kuh-SEED-uh) is a toxic dinoflagellate that has been associated with fish lesions and fish kills in coastal waters from Delaware to North Carolina. A natural part of the marine environment, dinoflagellates are microscopic, free-swimming, single-celled organisms, usually classified as a type of alga. The vast majority of dinoflagellates are not toxic. Although many dinoflagellates are plant-like and obtain energy by photosynthesis, others, including Pfiesteria, are more animal-like and acquire some or all of their energy by eating other organisms.

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?
Pfiesteria normally exists in non-toxic forms, feeding on algae and bacteria in the water and in sediments of tidal rivers and estuaries. Scientists believe that Pfiesteria only becomes toxic in the presence of fish, particularly schooling fish like Atlantic menhaden, triggered by their secretions or excrement in the water. At that point, Pfiesteria cells shift forms and begin emitting a powerful toxin that stuns the fish, making them lethargic. Other toxins are believed to break down fish skin tissue, opening bleeding sores or lesions. The toxins or subsequent lesions are frequently fatal to the fish. Fish may also die without developing lesions. As fish are incapacitated, the Pfiesteria cells feed on their tissues and blood. Pfiesteria is NOT an infectious agent like some bacteria, viruses, and fungi. Thus, fish are NOT killed by an infection of Pfiesteria, but rather by the toxins it releases, or by secondary infections that attack the fish once the toxins have caused lesions to develop. (back to the top)

How long do toxic Pfiesteria outbreaks last?
Toxic outbreaks of Pfiesteria are typically very short, no more than a few hours. After such an event, Pfiesteria cells change back into non-toxic forms very quickly, and the Pfiesteria toxins in the water break down within a few hours. However, once fish are weakened by the toxins, Pfiesteria-related fish lesions or fish kills may persist for days or possibly weeks. (back to the top)

Where has Pfiesteria been found?
where.gif (8805 bytes)Pfiesteria piscicida is known to occur in brackish coastal waters from the Delaware Bay to North Carolina. Other Pfiesteria-like organisms occur along the southeast coast from Delaware to the Gulf of Mexico. These organisms are believed to be native, not introduced species, and are probably common inhabitants of estuarine waters within their range. These microbes have not been found in freshwater lakes, streams, or other inland waters.

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?
Pfiesteria is not a virus, fungus, or bacterium. It is not contagious or infectious, and cannot be "caught" like a cold or flu. Any human health problems associated with the microbe stem from its release of toxins into river and estuarine waters.

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?
people fishing and boating in coastal waterd
Swimming, boating, and other recreational activities in coastal waters are generally safe. To be on the safe side, the following common-sense precautions are recommended:

  • Comply with state closures of water bodies and public health advisories. Do not go into or near the water in areas that are closed by the state.
  • If you notice significant numbers of fish that are dead or that exhibit lesions or other signs of disease, avoid contact with the fish and water, and promptly report the incident to your state's environment or natural resource agency. (back to the top)

Is Pfiesteria a harmful algal bloom?  How is it related to red and brown tides?
Most species of algae are not harmful. Algae are the energy producers at the base of the ocean's food web, upon which all other marine organisms depend. However, a few species of algae and other microbes can become harmful to marine life and to people under certain conditions. Scientists call such events "harmful algal blooms." Brown tides, toxic Pfiesteria outbreaks, and some kinds of red tides are all considered types of harmful algal blooms. Some harmful algal blooms, like toxic Pfiesteria outbreaks, can cause detrimental effects when the microbes are at low concentrations in the water and cannot be visibly detected. In other cases, like certain red and brown tides, harmful effects occur when the algae reach high concentrations that discolor the water. However, not all algal blooms that discolor the water are harmful -- many red tides appear to have no negative effects on marine life, people, or the environment.

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?
The exact conditions that cause toxic outbreaks of Pfiesteria to develop are not fully understood. Scientists generally agree that a high density of fish must be present to trigger the shift of Pfiesteria cells into toxic forms. However, other factors may contribute to toxic Pfiesteria outbreaks by promoting the growth of Pfiesteria populations in coastal waters. These factors include warm, brackish, poorly flushed waters and high levels of nutrients.

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?
State and federal agencies are working closely with local governments and academic institutions to address the problems posed by Pfiesteria. Federal agencies involved in the effort include the U.S. Environmental Protection Agency, the National Oceanic and Atmospheric Administration, the Centers for Disease Control and Prevention, the National Institute of Environmental Health Sciences, the Food and Drug Administration, the U.S. Geological Survey, and the U.S. Department of Agriculture. Together with the Maryland Departments of Health, Natural Resources, Environment and Agriculture these agencies are working to:

  • manage the risk of human health effects by monitoring and rapid response through river closures and public health advisories
  • direct funding and technical expertise to Pfiesteria-related research and monitoring
  • make current and accurate information widely available to the public
  • understand and address the causes of Pfiesteria outbreaks, especially the possible role of excess nutrients (back to the top)

Whom should I contact to report fish lesions, fish kills, or possible human exposure to Pfiesteria?
Maryland DNR is committed to providing up to date information to the public concerning the health of Maryland's waterways. If you have any questions that are not addressed by the information on our web site we encourage you to take advantage of the information we have provided on this page to assist you. Please read through all of the options below before making any calls.

Fish Health Hotline: 1-877-224-7229

If you would like to report a fish kill or have information for the Maryland Department of Natural Resources concerning sick fish you have caught or found call the toll free number listed above. Please read over the information below for specific information DNR needs to properly assist you.

Anglers can provide information that will help DNR monitor fish health throughout the Chesapeake Bay and its tributaries.

  • Examine fish for abnormalities.
  • Fish that look unhealthy in any way should be released.
  • Report abnormalities to the hotline after noting:
  1. species;
  2. location where caught;
  3. date and approximate time when caught;
  4. fishing gear used; and
  5. type of abnormality (describe in as much detail as possible, including area(s) of fish affected).
  • DNR reviews call data daily and determines if a Rapid Response Team of fish biologists should be deployed to the area, or if other investigation is necessary.
  • Fish abnormalities such as red scrapes, missing scales, and lesions can occur for many reasons, including: hook and release; nets; and bacterial infections.

Health Questions:

If you have questions about the safety of a waterway, water conditions, swimming or any other human health issues please contact the branch of the Maryland Department of Health and Mental Hygiene in the county you are concerned about.

Safety of Maryland Seafood:

Seafood safety is extremely important, Maryland has one of the strictest safety systems in place to insure that the food that comes out of the bay and its tributaries is the safest in the world. Contact the Maryland Department of Agriculture at 410-841-5820 if you have any concerns.

Questions Concerning Water Quality

The quality of water in the Chesapeake Bay and it's tributaries is an important component in the health of Maryland's aquatic habitats. If you have any questions regarding nutrient enrichment or general water quality in the affected systems or elsewhere in Maryland please contact DNR's Tidewater Ecosystem Assessment Division at 410-260-8630. (back to the top)

Where can I get more information about Pfiesteria?

State Pfiesteria, Fish Kill, or Related Health Effects Hotlines:
Maryland 1-877-224-7229
North Carolina 1-888-823-6915
Florida 1-800-636-0511
Delaware 1-800-523-3336
Virginia 1-888-238-6154

On the Internet:

Environmental Protection Agency

USDA National Agricultural Library

National Office for Marine Biotoxins and Harmful Algal Blooms

U.S. Geological Survey

Delaware Department of Natural Resources and Environmental Control http://www.dnrec.state.de.us/pff1.htm

Virginia Department of Health

North Carolina Department of Environment and Natural Resources http://www.esb.enr.state.nc.us/fishkill/killfact830.pdf

North Carolina Department of Health and Human Services http://www.schs.state.nc.us/epi/hab/faq.html

Academic Institutions:

University of Maryland Sea Grant- Fish Health in the Chesapeake Bay

Virginia Institute of Marine +Science

North Carolina State University Center for Applied Aquatic Ecology

North Carolina Sea Grant- Pfiesteria Research Results

Other resources for additional information

-Water Quality Improvement Act of 1998
University of Maryland College Park College of Agriculture and Natural Resources

-Maryland Department of Agriculture Agricultural Assessment Teams Pocomoke Water Quality Update
Three teams of agricultural assessment planners from the Maryland Departments of Agriculture and Environment are continuing their assessments of agricultural activities on the Lower Eastern Shore as part of a larger effort to understand the causes behind fish kills.

Read the Preliminary Characterization of Agriculture in the Pocomoke Watershed report.

-The Raleigh Report
Released at the end of Jan., 1998, this report represents the consensus of an expert scientific panel convened to examine Pfiesteria issues in North Carolina.  From North Carolina State University

-NCSU Aquatic Botany Laboratory Pfiesteria piscicida Homepage
Information on Dr. Burkholder's NCSU Aquatic Botany Lab where DNR sends the algal samples for analysis.

-Maryland Department of the Environment
Useful information concerning environmental and public health.

-Fish Health in the Chesapeake Bay
Learn about health issues of fish found in the Chesapeake Bay region.  From Maryland Sea Grant.

-Virginia Institute of Marine Science
Chesapeake Bay and beyond - Pfiesteria facts and information

-U.S. Environmental Protection Agency
Pfiesteria piscicida
web site.

(back to the top)

Fish Health

What is an abrasion?
An abrasion is a scrape, patch of missing or rough scales, or other superficial injury. Sometimes an abrasion may be accompanied by redness and/or blood. These are typically caused by handling or nets. As with humans, simple abrasions can become infected. (back to the top)

What is a lesion?
Lesion is a general term for the various effects of fish injuries or sicknesses, including the discoloration or deterioration of the skin or fins (scientific term is "skin/fin erosion"), and sores that may penetrate into the muscle or organs (scientific term is "ulcer"). Lesions may also be accompanied by redness and/or blood. Lesions may develop from external factors, such as bites by other fish or birds, abrasions that become infected, harmful algae blooms, or poisonous chemicals in the water. Lesions may also develop as an external indicator of an internal illness, such as weakening due to stressful water quality or temperature conditions.

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:

  • a fish kill with the majority of fish (particularly menhaden - bait fish sometimes known as alewives) exhibiting these lesions; and/or
  • fish swimming erratically, in distress with these lesions; and/or
  • high percentages of menhaden in one area exhibiting these lesions.

If you find any of these conditions, please contact the Fish Health Hotline at 1-877-224-7229.
(back to the top)

Is it safe to eat seafood?
picture of fish with lesions
YES. In general, it IS safe to eat seafood.

  • There has never been a case of illness from eating fish or shellfish exposed to Pfiesteria.
  • There is no evidence of Pfiesteria-contaminated fish or shellfish on the market.
  • All seafood products and processing facilities are required by law to have programs to ensure the safety of the fish and shellfish they sell. Seafood from restaurants, supermarkets, and other retailers is considered safe.
  • There is no evidence that illnesses related to Pfiesteria are associated with eating fish or shellfish.

To be on the safe side, the following common-sense precautions are recommended:

  • Comply with state closures of water bodies and public health advisories. Do not harvest or consume fish or shellfish from areas that are closed by the state.
  • Do not handle or consume fish that you have harvested that are dead or dying; that exhibit sores, peeling, lesions, or other signs of disease; or that were acting abnormally when caught.
  • If you notice significant numbers of fish that are dead or that exhibit lesions or other signs of disease, avoid contact with the fish and water, and promptly report the incident to your state's environment or natural resource agency. (back to the top)

What should I do if I catch a fish with a serious abnormality?
Fish with minor abrasions need not be reported. Citizens are encouraged to report fish with lesions. After noting where the fish was caught and a description of the lesion, throw the fish back. In most cases the fish will heal. Report the information to the Fish Health Hotline at 1-877-224-7229. Reports from the hotline are used to target follow-up investigations.

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?
A lesion is any sore, wound, or area of diseased tissue. There are many possible causes for fish lesions other than Pfiesteria and Pfiesteria-like organisms. These include physical injury in nets or traps, bites by other fish or birds, chemical pollutants, generally poor water quality, and infectious disease agents such as certain viruses, bacteria, and fungi. A fish kill is a situation in which many fish -- more than a few dozen -- die over a short period of time -- hours or days. Pfiesteria and Pfiesteria-like organisms are only one cause of fish kills on the southeast and Gulf coasts. Other causes include a lack of dissolved oxygen in the water, sudden changes in factors such as salinity or temperature, sewage or chemical spills, blooms of other kinds of harmful or toxic algae, infectious disease agents, and other environmental changes.

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?
Fish lesions are only one of the indicators used to judge whether a river should be closed or reopened. The State's protocol for closing rivers is based on the presence of significant numbers of dead fish or fish exhibiting erratic behavior as indicators of possible toxic Pfiesteria activity. Also, other possible explanations for the fish kills or fish health problems need to be evaluated as well as the testing of water samples for Pfiesteria-like organisms. All of these factors were considered in closing rivers in 1997. The State has taken the advice of environmental scientists and medical professionals in developing its closing and opening protocol as a precaution to protect public health. The scientific community is in wide agreement that these are the best indicators currently available. The State is aggressively working with researchers to develop new technologies that will identify Pfiesteria outbreaks sooner and with greater accuracy. (back to the top)

What has Maryland done to evaluate the various hypotheses regarding fish health, Pfiesteria, and its causes?
The State, along with its outside scientific advisors, has maintained an open and scientifically-based approach to identifying the causes of the observed fish health problems and fish kills, evaluating all scientifically credible theories. The role of fungus has been a subject of these evaluations since early in 1997. (back to the top)

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?
Menhaden do migrate long distances in Spring and Fall. While it is possible that infected or lesioned fish may move some distance, there is currently no scientific evidence to support a theory that the lesion outbreaks seen in 1997 in the three affected Maryland waterbodies developed in waters far from the Lower Eastern Shore. A more localized problem is suggested by the localized distribution of fish with lesions. Maryland scientists and other researchers will continue evaluate all theories related to lesion development. (back to the top)

The State of Maryland assisted in the development of these questions with the following groups:

  • United States Environmental Protection Agency
  • National Oceanic and Atmospheric Administration
  • United States Department of Agriculture
  • United States Geological Service
  • U.S. Department of Health and Human Services
  • Association of State and Interstate Water Pollution Control Administrators
  • State of Virginia
  • State of Delaware
  • State of North Carolina
  • State of Florida
 Pfiesteria Links:  FAQ | Monitoring | Publications | Contact Us
Pfiesteria piscicida | Pfiesteria shumwayae

Restoration and Protection | Bay Grasses | Harmful Algae | Bay Monitoring
Bay Life Guide | Bay Education

Return to the Maryland DNR Home Page