Study of Haematractidium scombri in Atlantic mackerel, Scomber scombrus.

The prevalence of Haematractidium scombri, an intraerythrocytic protozoan, was studied over a 3-yr period in Atlantic mackerel migrating off Chincoteague, Virginia. In 1974, 24%, in 1975, 42%, and in 1976, 45.3% of the fish examined were infected. Age-2 mackerel (measuring 25–28 cm fork length) were more frequently and more heavily infected than older fish. Adult mackerel from Boothbay Harbor, Maine, and from the bottom overwintering population in the Gulf of Maine also were infected; however, H. scombri was not found in blood smears of age-0 mackerel from Montauk, Long island, New York. Haematractidium was not found in tissue sections, but structures that might be exoerythrocytic stages were seen in kidney and spleen imprints.Key words: Haematractidium, protozoan, mackerel, Scomber