Pfiesteria piscicida is a recently-described toxic dinoflagellate that was originally isolated from North Carolina waters.
Pfiesteria piscicida has been documented from North Carolina, Delaware, and a fish farm in Maryland where it was associated with fish kills or the presence of fish with ulcers. Its extended distribution is unknown at this time because it is difficult to identify using standard techniques.
Pfiesteria piscicida has not been documented in Florida waters, although other dinoflagellates resembling this species have been found but their toxicity needs to be confirmed. These species are not Pfiesteria. One new species was found in the St. Johns River, Florida in the summer of 1997 in an area known to have a history of fish with lesions. This same new species has been found in the Pocomoke River, Maryland and in North Carolina waters in areas of active or historic fish kills and fish with ulcers.
In laboratory experiments, North Carolina State University scientists, Drs. JoAnn Burkholder and Ed Noga, have shown that P. piscicida can kill fish rapidly. Pfiesteria piscicida can cause lesions in fish (sloughing of skin and hemorrhaging) due to toxin exposure. Ultimately a fish disease develops known as "ulcerative mycosis" or "ulcerative disease syndrome" (UDS).
In this disease, first the fish is stressed by P. piscicida toxins, and then opportunistic pathogenic fungi, called water molds, or pathogenic bacteria invade breached external layers of the fish skin.
UDS is characterized by shallow to deep ulcers with >50 % of the ulcers appearing near the fish anal area. These ulcers, in advanced stages, are very dramatic because they can expose internal organs.
UDS and its characteristic ulcers have been documented since the 1980s from New York to Florida. In the 1980s there were several UDS events that resulted in studies and workshops to characterize the disease which can be seasonal or cyclical and may not occur every year.
Degrading water quality conditions in certain estuarine waters (UDS occurs in inshore areas of low to moderate salinity) are thought to be associated with disease outbreaks, but no definitive cause-effect relationship has been proven.
Also, in a laboratory setting, when cultures of P. piscicida were exposed to fish they produced high concentrations of toxins that caused North Carolina State University researcher Dr. Burkholder, and several of her colleagues, medical problems including memory loss and respiratory stress.
Because P. piscicida can stress fish and make them susceptible to UDS, because it can kill fish, and because it can cause neurological impairment in researchers working with it in the laboratory, this species is automatically being linked to fish kills and fish disease in Maryland and Virginia. In Maryland, it has been reported that a medical team has verified that people working on rivers where fish kills have occurred are suffering from medical problems similar to those of the laboratory-exposed NCSU researchers.
The fish skin sloughing toxin and the neurotoxin thought to be produced by P. piscicida may occur in other dinoflagellates or even other groups of organisms but not all of these toxins may be the same. This is certainly true for other toxic microalgae. We need to know what organisms are causing fish ulcers and possible human health problems. At the moment it is being assumed that all fish and potential public health problems in Maryland waters are being caused by Pfiesteria. The data is not there to support this assumption.
It is critical to determine the number and identity of toxic dinoflagellate species along the eastern seaboard. Different species of toxic dinoflagellates can produce very different toxic compounds each of which pose different threats to natural resources and public health. The toxins from each dinoflagellate species associated with areas known to have ulcerated fish need to be purified. These toxins can then be studied in a laboratory setting using mammalian models to determine cause - effect relationships and what dose causes the effects. We need to do the same studies with marine animals to determine lethal effects and susceptibility to disease.
Is there a marine resource problem? Yes. Fish kill events and the presence of fish with ulcers signal a stressed environment. What is causing these events, including the water quality conditions that lead up to the event, needs to be determined.
Is there a human health threat to people working on waterways with fish kills and fish with ulcers? An expert medical team in Maryland says yes for Maryland waters because of their latest findings. Does this mean that other inshore waterways in other states present a public health threat? Again, common sense says Maybe, but this cannot be confirmed until we know the organisms responsible, their distribution, their toxins, and the specific effects of those toxins.
What is Florida doing?
Florida Department of Environmental Protection (FDEP) senior research scientist Dr. Karen Steidinger and North Carolina State University professor Dr. JoAnn Burkholder described and named Pfiesteria piscicida based on specimens originally isolated from North Carolina.
FDEP scientists Drs. Jan Landsberg, Karen Steidinger, Earnest Truby, and Ms. Barbara Blakesley isolated and described the only other known Pfiesteria species which is as yet unnamed. It was isolated from a citizens tropical fish aquarium in Florida and associated with persistent fish kills in that aquarium. However, it is not known whether the Pfiesteria or a co-occurring parasite was responsible for the kill. It has not been identified as yet from natural waterbodiesear.
FDEP scientists have been searching for P. piscicida in Florida waters for several years, particularly in relation to fish kills or other marine mortalities. In summer 1996, a fish kill in the Indian River System was investigated. No P. piscicida were found but another known toxic dinoflagellate was identified. In 1996, during the manatee die-off in southwest Florida waters, P. piscicida was also looked for but not found. Again, it was not Pfiesteria but another known dinoflagellate whose toxins were identified in dead manatee organs. In both cases, there was public speculation that P. piscicida was the cause.
FDEP scientists working with cultures supplied by the National Marine Fisheries Service Beaufort Laboratory in North Carolina, have identified those cultures as belonging to a new species; they are not a Pfiesteria. Two of the isolates were from historic fish kill and disease areas in North Carolina's Pamlico and Neuse Rivers, the other from an experimental tank where active fish kills were occurring. The identifications were requested because this research group needed to confirm whether their material was P. piscicida or another species. This same species has been identified from waters having fish kills and disease in Maryland and from waters having fish with ulcers in Florida.
FDEP scientists Drs Steidinger, Landsberg, and Truby from Florida have analyzed water and sediment samples from Maryland waters at the request of Maryland Sea Grant and Maryland Department of Natural Resources. Last year, one sample from an aquaculture fish farm had a bloom of P. piscicida. Other samples from natural waters of Maryland, mainly the Pocomoke River, have not yielded P. piscicida, but have revealed several new species morphologically similar to P. piscicida. These species are not Pfiesteria. Each of these species need to be characterized and confirmed for toxicity. This does not mean that they all produce the same toxins as Pfiesteria or that they all produce toxins.
FDEP scientists have agreed to look at Virginia samples at the request of several Virginia scientists.
FDEP scientists are willing to hold a workshop to teach eastern seaboard state and university scientists how to identify P. piscicida and how to differentiate this species from other species. Such a workshop is not currently funded. This will allow individual states to determine the distribution of these dinoflagellates in their waters. Also, before molecular probes can be developed for easier identification of species and toxins, we have to know what species we have isolated and cultured.
FDEP have offered to share their cultures of these organisms with other scientists so their physiology, life cycle, toxins, and bloom dynamics can be studied by other experts. This will advance the state of knowledge of the newly-found species.
FDEP scientists are currently working with other scientists at the Bigelow Laboratory for Ocean Sciences, the National Marine Fisheries Service Beaufort Laboratory, and the North Carolina State University to characterize new species found in association with fish kills and areas where fish have ulcers.
FDEP scientists in cooperation with other Florida and North Carolina scientists have been involved in characterizing fish ulcer diseases as well as other fish lesion diseases since the 1980s.
FDEP scientists have been working with staff of the St. John's River Water Management District. Posters requesting information on fish with ulcers will be posted in areas along the St. John's River. These posters also notify the public of the state wide 1-800 fish kill hotline number, so that information regarding the distribution of fish with ulcers can be obtained. Additional surveys are being sent out to the fishing public.
FDEP scientists will present a seminar on Pfiesteria and other pertinent research at the St. John's River Water Management District at the end of October. A roundtable will be held afterward to discuss and plan future needs and potential natural resource and public health risks.
FDEP scientists have been working with scientists at the National Marine Fisheries Service Laboratory in Miami to study the distribution of fish with ulcers in the St. Lucie River. As with the St. John's River, fish in the St. Lucie River have been reported with ulcers since the 1980's.
No Pfiesteria has been found in the St. Lucie River.
Prepared by Karen Steidinger and Jan Landsberg, FDEP 9/17/97
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