CERATOMYXA-SPARUSAURATI (PROTOZOA, MYXOSPOREA) INFECTIONS IN CULTUREDGILTHEAD SEA BREAM SPARUS-AURATA (PISCES, TELEOSTEI) FROM SPAIN - ASPECTS OF THE HOST-PARASITE RELATIONSHIP

Ceratomyxa sparusaurati infection was studied in gilthead sea bream fr om different mariculture systems of Spain. Culture conditions were fou nd 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 fro m the latter system. but no clear seasonal pattern was observed in the remaining fish groups in any system. A statistically significant depe ndence between infection prevalence and host weight was observed in so me fish groups. Different degrees of histopathological damage were not ed in the infected gallbladders, mainly involving swelling, vacuolizat ion, and sloughing of the epithelial cells. Transmission electron micr oscope observations of the infected tissues demonstrated a characteris tic protrusion of the epithelial cell surface and mitochondrial altera tions. In fish from stocks showing external disease signs and tricklin g mortalities, parasite stages invaded other organs and were responsib le for cell-mediated host reaction and important tissue injuries. Ther efore, C. sparusaurati can be considered a potential threat for some S parus aurata-growing systems.