Low incidence of Pfiesteria this season
Pfiesteria Monitoring Activities:
The three rivers affected in 1997, the Chicamacomico River, Kings Creek (Manokin River) and the Pocomoke River, are being monitored as well as five other systems (Nanticoke River, Wicomico River-Eastern Shore and Big Annemessex in the Chesapeake Bay and Trappe Creek and St. Martin River in the Coastal Bays) that may be susceptible to outbreaks. Water quality and fish populations are also being evaluated Bay-wide through ongoing fisheries surveys and the DNR's Chesapeake Bay Monitoring Program. The following summary updates monitoring and environmental conditions for the spring and early summer 1999 sampling season.
Preliminary results are now available on possible causes for the small percentages of lesioned menhaden observed in the Lower Eastern Shore Rivers this year. Menhaden examined to date were collected in May and early June from the following tributaries: Nanticoke River, Fishing Bay, Wicomico River, and Pocomoke River. The samples taken on the Pocomoke on June 9 were collected when 66 out of 5065 (1.3%) menhaden showed some form of a lesion. The fish samples have been processed and are awaiting final diagnosis. Many of the menhaden that have been examined by pathologists to date had a sporozoan (parasite) infection in their muscles. Frequently, these parasites were present in the muscles around the head, gills and eyes. This infection ranged from quite mild with only a few muscle cells containing parasites, to severe with parasites causing distension and disruption of the cells. In the most severe cases, these parasites caused a raised lesion on the surface of the skin or a space-occupying lesion in the gills. Positive identification of this parasite is pending and will be based on histological (microscopic) appearance. Transmission of these parasites is not completely understood, but a possible mode of infection is direct entry in the mouth area or indirect entry via an intermediate host. High concentrations of parasites may occur in poorly flushed waterways.
Two tributaries of the Chesapeake Bay are currently experiencing major sustained fish kills as a result of severely depleted dissolved oxygen levels. Thousands of fish continue to die in the shallow, sub-tributaries of Magothy and Patapsco Rivers; over 200,000 fish have succumbed thus far. Drought conditions are causing low dissolved oxygen conditions, common in bottom water layers in summer, to occur in surface layer waters as well; several natural and human induced factors have acted together to intensify this effect. Dissolved oxygen readings have been recorded near zero in many locations. The die-off is expected to continue as long as summer drought conditions prevail in the region.
Fish kills involving yellow perch were also reported on Middle River on July 7. Maryland Department of the Environment believes these to be a result of high water temperatures (29 to 32 C, or 84 to 90 F) and increased salinity. Yellow perch are extremely temperature sensitive and were the dominant species affected in this kill. Other species, such as white perch, did not seem to be affected. A reminder - please report fish kills, sick fish or fish with lesions to the Maryland Fish Health Hotline at 1-888-584-3110.
Dr. David Oldach (University of Maryland Biotechnology Institute) has been examining water samples with an experimental genetic technique designed to rapidly identify the presence of Pfiesteria piscicida. As of July 7, results had been reported for 139 water samples collected on 17 different tributaries of Chesapeake Bay and Maryland's coastal bays. Only one sample, collected June 24 in the Shelltown region of the Pocomoke River, was positive for Pfiesteria piscicida. This technique does not differentiate between the toxic and non-toxic forms of the organism, and the lack of distressed fish during this time strongly suggests that the test detected the presence of Pfiesteria in one of its non-toxic forms. These results are not a reason for great concern, as previous experience has already demonstrated that non-toxic Pfiesteria exists in the lower portions of the Pocomoke River. Additional sampling of the lower Pocomoke for Pfiesteria and associated algal species will be conducted during the week of July 12.
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