Vol. 20: 7-13, 1994 DISEASES OF AQUATIC ORGANISMS Dis. aquat. Org. Published October 13 An intranuclear microsporidian in lumpfish Cyclopterus lumpus J. E. Mullins, M. Powell, D. J. Speare, R. Cawthorn Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island. Canada CIA 4P3 ABSTRACT: Chronic mortalities in lumpfish Cyclopterus lumpus raised in a saltwater recirculation system were associated with the presence of an intranuclear rnicrosporidian. Morphologic changes were characterized by infdtration of lymphocyte-like cells predominantly in the renal interstitium and also in the spleen, liver, gills, stomach, pyloric caecae, heart, ovary and mesenteric fat. Affected cell nu- clei contained 1 to more than 6 spherical to oval eosinophilic bodies which stained poorly with hema- toxylin and eosin and Giemsa. Ultrastructurally, spores were ovoid (2.1 X 1.0 pm) with a polar tube with 11 turns. The morphology of these spores place them in the genus Enterocytozoon. These spores resem- ble E. salmonis in salmonids, and Microsporidia rhabdophilia in the rodlet cells of salmonids. KEY WORDS: Microsporidian . Enterocytozoon . Lumpfish INTRODUCTION sporihan associated with chronic mortalities in salt- water cultured lumpfish Cyclopterus lumpus. Microsporidia are common intracellular protozoan parasites observed in many species of animals. Although numerous species occur in fish, there are few MATERIALS AND METHODS reports of rnicrosporidia found within the host cell nu- cleus. Modin (1981) described Microsporidium rhabdo- Samples of moribund fish from a saltwater recircula- philia in the nuclei of rodlet cells of several species of tion facility were submitted to the Fish Health Unit, salrnonids in fresh water. However, the presence of Atlantic Veterinary College, Charlottetown, PEI, these parasites was not associated with clinical signs or Canada, for histopathological examination on 4 occa- disease. sions (27 November 1992; 14 January, 11 February and Mortalities and disease associated with Entero- 8 March 1993). A total of 17 fish were examined. Of cytozoon salmonis within the host cell nucleus were these, 15 were 0 to 12 mo, 1 was older than 1 yr and described in chinook salmon Oncorhynchus tshawyt- 1 was older than 2 yr. scha in fresh water (Hedrick et al. 1990, Morrison et al. Portions of liver, kidney, gill, heart, spleen, intestine, 1990) and in salt water (Elston et al. 1987).These infec- pyloric caecae, gonads and brain were fixed in Bouin's tions were characterized by severe anaemia (Elston et solution for 12 to 24 h. Tissue samples were dehy- al. 1987) and lymphoblastosis (Hedrick et al. 1990, drated in ethanol, embedded in paraffin wax and sec- Morrison et al. 1990). The cell type involved was in- tioned at 5 pm thickness. Sections were stained with itially believed to be a haematopoietic precursor hematoxylin and eosin, Giemsa, toluidine blue and (Elston et al. 1987) but was later determined to be a periodic acid Schiff (PAS) (Luna 1968). lymphocyte precursor (Hedrick et al. 1990). Internal organs from a separate submission of frozen This report describes the clinical, histopathological fish were processed following the plankton centrifuge and ultrastructural features of an intranuclear micro- method (O'Grodnick 1975) and examined with a Zeiss O Inter-Research 1994