Bonamia has also caused 40%-60% mortalities in two or three stocks of O. lutaria held on a mussel farm 800 km north east of Foveaux Strait. Mass winter mortalities have been reported among native rock oysters, Saccostrea glomerata , until recently the basis of oyster farming. Similar blisters occur in the shell of the currently farmed Crassostrea gigas and may be associated with ectosymbionts. Mortalities and disease have not been reported in the intensively-farmed green-lipped mussel (Perna canaliculus ) or blue mussel (Mytilus edulis aoteanus ), but digenean sporocyts are common in these species. All these bivalve species may contain the copepod, Pseudomyicola spinosus , in the gut, but pathogenicity has not been demonstrated. Pea-crabs are also common as ectosymbionts, but in Perna the gregarine Nematopsis cycles through the mussel and crab. The general health of the stocks is discussed.