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Fish Health, Fungal Infections, and Pfiesteria: The Role of the U.S. Geological Survey

By Vicki Blazer, Scott Phillips, and Edward Pendleton

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Excerpt From Introduction

The increasing incidence of fish-health problems, ranging from small external sores and lesions to large-scale fish kills in the Chesapeake Bay and other Mid-Atlantic estuaries, is of growing concern to natural resource managers and residents of the Chesapeake Bay watershed. Fish kills have been reported in North Carolina since the early 1990's. Reports of skin lesions on fish in the summer and fall of 1996 and 1997 in the Pocomoke River, Maryland and other tributaries of Chesapeake Bay stimulated a great deal of public and scientific interest. These skin lesions ranged from small pinpoint hemorrhages to abrasions to deep ulcers. In addition, there were two fish kills, involving primarily Atlantic menhaden, in the Pocomoke River during August 1997. The fish kills, as well as the variety of fish lesions, have been blamed on the presence of a toxic dinoflagellate, Pfiesteria piscicida, or Pfiesteria-like dinoflagellates. The occurrence of Pfiesteria has been attributed to nutrient enrichment, warm water temperatures, moderate to high salinity, and fish excretions (Burkholder and Glasgow, 1997).

While Pfiesteria has been identified as a potential cause of fish kills in the Chesapeake Bay and other estuaries, there is growing evidence that other pathogens also are causing lesions in fish in the Bay. Skin lesions in fish can be caused by a variety of infectious and noninfectious insults. Lesions commonly are caused by opportunistic pathogens, which infect weakened or stressed hosts. These pathogens, which include bacteria, fungi, viruses, and parasites, may gain entry because of impaired immune or disease resistance factors, or because the natural defense mechanisms of the skin are impaired or breached.

Several State and Federal agencies, including the U.S. Geological Survey (USGS), are currently working to understand the relation between Pfiesteria and other pathogens to fish and human health, and to natural and man-induced factors (such as nutrients and sediment). This information will be used to help formulate management solutions to the problem.

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