Survey for the oyster parasites Bonamia, MSX, and Dermo in Texas bay systems

Texas Parks and Wildlife Department restricts movement of American oysters (Crassostrea virginica) from one Texas bay system to another because of potential disease transfer and genetic differences in natural oyster stocks. Oyster diseases, such as Bonamiosis, which was found serendipitously in 2007 in Florida waters, and MSX (Haplosporidium nelsoni) have not been characterized in Texas bays. Therefore, it is prudent to periodically examine Crassostrea virginica and other species (e.g., Ostrea equestris and Isognomon sp.) from different Texas bays for the presence of the causative agents of these diseases, i.e., Bonamia spp. and Haplosporidium nelsoni, as well as known diseases such as Perkinsus marinus. American oysters (n=30/bay) were collected from October to December 2016 in Copano Bay, San Antonio Bay, Matagorda Bay, Galveston Bay, and Sabine Lake. In addition, 89 historical American oyster tissue samples collected from 2010 and 2011 in Aransas Bay and Copano Bay in Texas were assessed. Finally, 38 flat tree oysters (Isognomon alatus) were collected in December 2017 from Lower Laguna Madre in Port Isabel, Texas. All specimens were assessed by PCR and histology for the presence or absence of Bonamia sp., Haplosporidium nelsoni, and Perkinsus marinus. No Bonamia spp. or H. nelsoni was detected in any American or flat tree oyster, but on average 15% of the 2016 American oyster samples and 27% of the 2010-2011 American oyster samples contained P. marinus. Sanger sequencing of isolated DNA was performed on samples that were positive for Dermo as well as the positive Bonamia sp. and H. nelsoni controls, which confirmed results. These results serve as a point reference that indicate Bonamia spp. and H. nelsoni are still not currently present in Texas bays, but continued biennial monitoring is suggested.