Pathogens in Crassostrea ariakensis and other Asian oyster species: implications for non-native oyster introduction to Chesapeake Bay

With the drastic decline of eastern oyster Crassostrea virginica populations in the Chesapeake Bay due to over-fishing, diseases and habitat destruction, there is interest in Maryland and Virginia in utilizing the non-native oyster species Crassostrea ariakensis for aquaculture, fishery resource enhancement, and ecological restoration. The International Council for the Exploration of the Sea (ICES) recommends that non-native species be examined for ecological, genetic and disease relationships in the native range prior to a deliberate introduction to a new region. Therefore, a pathogen survey of C. ariakensis and other sympatric oyster species was conducted on samples collected in the PR China, Japan and Korea using molecular diagnostics and histopathology. Molecular assays focused on 2 types of pathogens: protistan parasites in the genus Perkinsus and herpesviruses, both with known impacts on commercially important molluscan species around the world, including Asia. PCR amplification and DNA sequence data from the internal transcribed spacer region of the rRNA gene complex revealed the presence of 2 Perkinsus species not currently found in USA waters: P. olseni and an undescribed species. In addition, 3 genetic strains of molluscan herpesviruses were detected in oysters from several potential C. ariakensis broodstock acquisition sites in Asia. Viral gametocytic hypertrophy, Chlamydia-like organisms, a Steinhausia-like microsporidian, Perkinsus sp., Nematopsis sp., ciliates, and cestodes were also detected by histopathology.