TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 Perkinsus Spp. Infections In The Softshell Clam Mya arenaria Shawn M. McLaughlin1, Adel Shaheen2, Ben D. Tall3, Shaban I. Kotob4, and Mohamed Faisal4 1National Ocean Service, Center for Coastal Environmental Health and Biomolecular Research, Cooperative Oxford Laboratory, 904 S. Morris St., Oxford, MD 21654; 2Faculty of Veterinary Medicine at Moshtohor, Benha, Egypt; 3Food and Drug Administration, Microbial Ecology Branch, 200 C St., SW, Washington, DC 20204;4Virginia Institute of Marine Science, School of Marine Science, The College of William and Mary, Gloucester Point, VA 23062 Significant losses of bivalves reported worldwide have been associated with infections by protozoans of the genus Perkinsus. Perkinsus marinus is a well-known pathogen of the eastern oyster Crassostrea virginica, and causes severe mortalities along the Atlantic and Gulf coasts. Epizootiological studies show Perkinsus spp. infections to be on the rise in another economically and ecologically important species of the Chesapeake Bay, the softshell clam Mya arenaria. Recently, two Perkinsus spp. were isolated from the hemolymph (H49) and gill tissue (G117) of softshell clams collected from the Chester River, Maryland. Morphology, life cycle, enlargement in thioglycolate medium, reactivity with anti- P. marinus, and gene sequencing studies showed the two isolates to possess characteristics of Perkinsus species. There were, however, striking morphologic differences between the H49 and G117 isolates. Except for their larger size, H49 trophozoites and schizonts exhibited the characteristic morphology of P. marinus and divided by schizogony. Conversely, the G117 isolate shared morphologic similarities with P. atlanticus. The life cycle of the G117 isolate is unique in exhibiting both vegetative forms and prezoosporulation stages in the same culture. Additional molecular studies have confirmed the relatedness between H49 and P. marinus and the likelihood of G117 being a new species. Zoosporulation studies were conducted by placing fresh isolates of G117 into sterile seawater. Pre-zoosporangia matured into zoosporangia following contraction of the cytoplasm and successive bi-partition of the protoplast. Zoosporangia developed discharge tubes 48 hrs post-incubation, and hundreds of zoospores were released two days later and continued to be released for over a week. Electron microscopy studies of fixed zoospores revealed a biflagellate with features unique to Perkinsus species. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page