HAPLOSPORIDIUM-NELSONI (MSX) EPIZOOTIC IN THE PISCATAQUA RIVER ESTUARY (MAINE NEW-HAMPSHIRE, USA)

A major epizootic of Haplosporidium nelsoni occurred during 1995 in th e Piscataqua River Estuary, near the northern distributional limit of the parasite. Prevalence of N. nelsoni in samples of oysters, Crassost rea virginica, collected between 5 September and 18 December 1995 from sites in Maine and New Hampshire ranged from 15 to 81%, with up to 50 % systemic infections. Associated proportions of dead oysters ranged f rom 25 to 83%. The epizootic was most likely triggered by unusually wa rm and dry climatic conditions in 1995 that resulted in a temperature and salinity regime in the estuary that favored the parasite.