Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Two groups of juvenile summer flounder maintained at 5�C were experimentally infected with the hemoflagellate Trypanoplasma bullocki. Another group maintained at 5�C was not infected. The water temperature of one infected group was raised stepwise to 12�C, 18�C, and 24�C for 2 to 3 weeks at each level. The other infected group was maintained at 5�C for 12 weeks, the duration of the experiment. In addition, juvenile flounder were collected over a temperature range of 6�C to 22�C from February to June, 1982 to monitor natural infections. Live T. bullocki were incubated in plasma from fish at each temperature to monitor the host's humoral response. Trypanoplasmacidal lysis occurred in experimental infections maintained at 24�C and in natural infections over a range of 10�C to 22�C. Complete elimination of trypanoplasms occurred in experimental infections at 24�C and in natural infections at 22�C. Differences in temperature where lytic activity occurred was mainly attributable to the short time exposure of experimental infections to increasing temperatures in contrast to that occurring in nature. Trypanoplasmacidal lysis with increasing water temperatures in flounder indicates that the fish's humoral immunity is responsible for the annual spring decline in prevalence and eventual elimination of T. bullocki infections. Elevated levels of macroglobulins were detected in the sera of juvenile flounder recovering from T. bullocki infections, and this may be associated with antibody production in response to the parasite.



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