TWENTY-FIFTH ANNUAL EASTERN FISH HEALTH WORKSHOP MARCH 10-13, 2000   Immunogenetics Of Resistance To The Myxozoan, Ceratomyxa shasta     Jerri Bartholomew1, Margo Whipple1, Don Campton2, Sandra Ristow3 and Gary Thorgaard3     1Department of Microbiology, Oregon State University, Corvallis, OR 97331; 2U.S. Fish and Wildlife Service,  Abernathy Salmon Culture Technology Center, 1440 Abernathy Rd, Longview, WA 98632; 3 School of Biological Sciences, Washington State University, Pullman, WA 99164       One of the best-documented examples of heritable resistance in fish occurs in populations of salmon and trout that have evolved in the presence of the myxozoan parasite Ceratomyxa shasta. Recent advances in our knowledge of C. shasta’s life cycle, development of molecular tools for its identification and the marked differences in susceptibility to C. shasta among conspecific populations, make this parasite a good candidate for studying the mechanisms involved in disease resistance.  Our long-term strategy for identifying these mechanisms is to correlate resistance with mapped genetic markers, then to determine the innate immune responses associated with this resistance.  To accomplish these aims, clonal lines with divergent resistance to C. shasta and a genetic map based upon clonal line crosses have been developed in the Thorgaard laboratory.  The hybrid clones produced from these lines were tested for their resistance to C. shasta.  Sixty days following challenge, 100 % (n = 22) of the susceptible hybrid clones had died from infection by C. shasta; mortality in the resistant hybrid line was 4% (n = 25). In addition, we demonstrated that resistance to C. shasta is passed as a dominant trait among progeny of crosses between two outbred strains of rainbow trout, the resistant Klamath strain, and the susceptible Cape Cod strain.  Key to mapping disease resistance genes will be identifying the innate immune responses that vary between the strains.  Indicators of cellular responses - phagocytic activity and nonspecific cytotoxic cell (NCC) activity - in resistant and susceptible fish were compared and were not found to correlate to infection by C. shasta. Capacity to produce specific antibodies against the trophozoite stage of C. shasta was investigated in the susceptible (Cape Cod) and resistant (Klamath) strains.  Antibody against parasite antigens was detected; however, the response was not consistent between fish from either the resistant or susceptible strain.     Return to 25th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page