Studies on Amyloodinium ocellatum (Dinoflagellata) in Mississippi Sound: Natural and Experimental Hosts

Four species of parasitic dinoflagellates have been found to occur naturally on the gills and fins of Mississippi Sound fishes: Amyloodinium ocellatum (Brown 1931) Brown and Hovasse 1946, Oodinium cyprinodontum Lawler 1967, and two undescribed species. Sixteen of 43 species of fishes examined had natural gill infections of A. ocellatum. Seventy-one of 79 species of fishes exposed to A. ocellatum dinospores were susceptible, and succumbed, to the dinoflagellate. Eight did not die even though exposed to numerous dinospores. The most common signs in an infested fish were spasmodic gasping and uncoordinated movements. Trophonts of A. ocellatum were found on the gills, skin, fins, eyes, pseudobranchs, membranes of the branchial cavity and around the teeth; and in the lateral line pits, nasal passages, esophagus, and intestine of experimentally infected fishes. The dinoflagellate causes extensive mortalities of fishes held under closed-system mariculture conditions