Glomerular disease associated with Polysporoplasma sparis (Myxozoa) infections in cultured gilthead sea bream, Sparus aurata L. (Pisces : Teleostei)

Polysporoplasma sparis infection was studied in gilthead sea bream from dif ferent mariculture systems of the Spanish coasts. Culture conditions influe nced the infection dynamics, as the parasite appeared only in semi-intensiv e cultures and was not found in intensive closed systems nor in open ones. No clear seasonal pattern was observed. No fish weighing less than 51 g was found parasitized in any group. A statistically significant dependence bet ween infection prevalence and host weight was observed in some growing stoc ks. Light and transmission electron microscope observations revealed seriou s damage in the trunk kidney. Glomerular disease was provoked by the progre ssive occupation of the glomerular capillaries by P. sparis spores. Tubular epithelial cells were also affected. Inflammatory responses appeared towar ds the end of the infection, and consisted mainly of melanomacrophages and eosinophils. Rodlet cells were common close to infected capillaries and deb ris of rodlet sacs formed a belt encircling capillary vessels. Cytochemistr y demonstrated the lipidic nature of these sacs and the glycogen and glycop rotein composition of the cytoplasmic granules of rodlet cells.