Fish Health investigations in progress in Chesapeake Bay, no evidence of toxic Pfiesteria being found

August 21, 2001


This is the fifth report of the 2001 season.

Fish Health and Pfiesteria monitoring.
Wetipquin Creek, Nanticoke River
: On August 6, 74 of 690 menhaden captured during routine monitoring of the fish community by Maryland Department of Natural Resources Resource Assessment Service exhibited ulcers.  No Pfiesteria was present in three water samples collected at the site.  Subsequent fish sampling has not revealed any further fish health problems. 

Middle River: On August 7th, 50% (7 of 14) routine monitoring water samples tested positive for Pfiesteria with the genetic probe by Dr. David Oldach’s laboratory at University of Maryland Biotechnology Institute. Five menhaden captured in the region appeared healthy. This is the same region where on July 16th, 9 of 14 samples tested positive for the presence of Pfiesteria.  This region was the scene of a prolonged fish lesion event and numerous water samples that were positive for P. piscicida presence during August and September 1999, although there was no evidence of active toxicity.

Back Creek, Manokin River, area of Millard Long Road bridge: There were 15 of 27 (55.6%) menhaden collected during routine monitoring on August 9th that had ulcers. The area was resampled on August 15th and 52.1% (241 of 463) of the menhaden collected again showed ulcers. The area was revisited on August 20th and approximately 17% (71 of 420) of the menhaden continued to show ulcers although the percentage has declined relative to the last two weeks.  Each of the two water samples collected each day tested positive for Pfiesteria but light microscopy results indicated low levels of Pfiesteria-like cells. 

Colgate Creek, Patapsco River: Evidence of a fish kill and fish under stress were observed on Colgate Creek on August 6th and was investigated by Maryland Department of the Environment.  Extremely high dissolved oxygen conditions associated with algal bloom conditions were measured at the site and water samples tested for nutrient conditions showed high concentrations of ammonia. High ammonia concentrations can be stressful or toxic to fish.  Water samples collected on August 6th also show one of three testing positive for Pfiesteria, however, presumptive counts for Pfiesteria-like cells under light microscopy were recorded at low densities.  Follow-up sampling on August 9th and 15th revealed no further fish health problems, but three of six water samples were positive for the presence of Pfiesteria at low levels.  There has been no evidence of toxicity in one of these samples subjected to a fish bioassay at Dr. JoAnn Burkholder’s laboratory at North Carolina State University

Marumsco Creek, Pocomoke River: A fish kill report was investigated on August 16th where a total of approximately 16,000 menhaden were found dead. The kill was estimated to have occurred two days earlier based on the state of decomposition of the fish. None of the fish appeared to have ulcers and low oxygen conditions were found at the investigation site (1.3 mg O2/L at one site and 2.8 mg O2/L at a second site; at least 5 mg O2/L is typically associated with healthy water quality conditions for most fish). A sample of seven white perch and four killifish netted at the site looked healthy. No Pfiesteria was present in water samples tested with the genetic probe at Dr. Oldach’s lab, University of Maryland Biotechnology Institute.

Overall results from the genetic testing of water samples for Pfiesteria.
As of August 16th, 9% (45 of 541) of routine monitoring and rapid response samples collected during 2001 were associated with the presence of Pfiesteria piscicida and P. shumwayae.

General notes on water quality condition.
Flow conditions for the Chesapeake Bay have been below average since May and with the exception of April, flows into the Bay are below average for the year. Since August 15th, conditions at Nassawango Creek, Snow Hill, MD on the Pocomoke River however are 3-5 times the median discharge levels for the 51-year data set for the area.

Salinities have declined in recent days in response to the increased flows as can be seen at the continuous monitoring stations at Rehobeth on the Pocomoke River, Drawbridge at the Chicamacomico and Decoursey Bridge on the Transquaking River (see charts below).


A reminder - please report fish kills, sick fish or fish with lesions to the Maryland Fish Health Hotline at 1-888-584-3110.

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