A novel Bonamia sp. discovered in Bogue Sound, NC, has recently emerged as a parasitic threat to the Asian oyster Crassostrea ariakensis. Because this oyster is being considered for introduction to the mid-Atlantic region, more data are needed to better evaluate the risks associated with this parasite. Field observations collected from North Carolina and information on other Bonamia spp. suggest an affinity for higher salinities, and direct transmissibility; in the absence of explicit experimental tests, however, this is largely hypothetical. Consequently, we used laboratory trials to test the direct transmissibility and the persistence of Bonamia sp. in infected triploid C. ariakensis transferred to and maintained at three salinities, 10, 20, and 30 psu for at least 15 wk. Under these experimental conditions, there was no evidence of direct Bonamia sp. transmission. Average parasite intensity in infected oysters transferred to and maintained at 10 and 20 psu decreased compared with oysters placed at 30 psu. At the same time, host mortality was significantly reduced at salinities below 30 psu. These experimental results suggest that the survival of Bonamia sp. in C. ariakensis may be limited in mesohaline areas. The persistence, pathogenicity, and transmission of Bonamia sp. under polyhaline conditions will need to be further evaluated to better describe the geographic areas at risk in the event of C. ariakensis introduction.