Ceratomyxa sparusaurati (Protozoa:Myxosporea) infections in cultured gilthead sea bream Sparus aurata (Pisces:Teleostei) from Spain: aspects of the host-parasite relationship.

Ceratomyxa sparusaurati infection was studied in gilthead sea bream from different mariculture systems of Spain. Culture conditions were found to influence the infection dynamics. Total prevalences ranged from 0 in a closed system to 59.9% in a Mediterranean semi-intensive farm. Prevalence was significantly lower in summer in a restricted group from the latter system, but no clear seasonal pattern was observed in the remaining fish groups in any system. A statistically significant dependence between infection prevalence and host weight was observed in some fish groups. Different degrees of histopathological damage were noted in the infected gallbladders, mainly involving swelling, vacuolization, and sloughing of the epithelial cells. Transmission electron microscope observations of the infected tissues demonstrated a characteristic protrusion of the epithelial cell surface and mitochondrial alterations. In fish from stocks showing external disease signs and trickling mortalities, parasite stages invaded other organs and were responsible for cell-mediated host reaction and important tissue injuries. Therefore, C. sparusaurati can be considered a potential threat for some Sparus aurata-growing systems.