Microsporidiosis in European sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata) farmed in Italy.

The phylum Microsporidia contains several species responsible of serious diseases in farmed fish. Some cases of intestinal and muscular microsporidiosis respectively in European sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata) farmed in intensive systems in Italy are here described. Thirty-four sea bass from 4 different inland farms, all strongly emaciated, showed under dissection microscope the presence of whitish nodules of about 300-500 μm in diameter in the intestinal tract. At higher magnification (40x-100x) the nodules appeared filled of spores measuring 2-2.5 x 4-4.5 μm, ovoid in shape with a large posterior vacuole occupying more than half part of the spore body. The histology showed the nodules as xenomas, i.e. hypertrophic infected host cells of lamina propria, with a well-defined eosinophilic wall. The persistence of hypertrophic and/or fragmented nucleus of the host cell and the scattered presence of mature spores among several developmental stages were noticed. Xenomas were present mainly in lamina propria, single or sometimes clustered, and rarely in the submucosa. The highly infected areas showed the epithelium sloughing-off. Inflammatory reactions were not observed around the xenomas during their early developmental phases, while mature xenomas were surrounded by granulomatous reaction with necrosis. The morphological and histological features indicated the parasites as Glugea spp. Concerning gilthead sea bream, the presence of microsporidian cysts in the trunk muscle was detected in 25 fish farmed in inshore floating cages. The cysts were ovoid or ellipsoidal in shape, measuring 1-10 x 1-2 mm and at microscopic examination resulted filled of microsporidian spores. These were ovoid, 2.5-3 x 3.5-4.5 μm, with a huge posterior vacuole. At the histological examination the cysts appeared composed of aggregates of spores, surrounded by a slight inflammatory reaction. Macrophages were only observed in presence of mature cysts. Severe regressive changes were observed in the skeletal muscle tissue, with atrophy, myonecrosis and haemorrhages. On the basis of the morphology of the spores and the histopathological lesion the parasite could be referred to the genus Kabatana. The sanitary implications of these microsporidioses for Mediterranean mariculture will be discussed.