Survey of bacterial pathologies affecting farmed gilt-head sea bream ( Sparus aurata L.) in southwestern Spain from 1990 to 1996

A bacteriological survey in three fish farms with intensive culture of gilt-head sea bream ( Sparus aurata L.) was conducted in southwestern Spain (provinces of Cadiz, Malaga, and Huelva) from 1990 to 1996. All the disease problems occurring during this period in the S. aurata were investigated, focusing on the isolation, characterization, antimicrobial resistance and pathogenicity of the bacterial isolates affecting the fish. The main pathogenic microorganisms isolated were Vibrio (67.8%), Pseudomonas (13.5%), Photobacterium damsela subsp. piscicida (6.7%), Cytophaga/ Flexibacter-like bacteria (4.8%), Aeromonas (0.5%), and Gram positive bacteria (6.7%). Although the highest percentages of isolates corresponded to Vibrio and Pseudomonas spp., the strains of P. damsela subsp. piscicida and Cytophaga/ Flexibacter-like bacteria caused epizootics with highest degree of mortalities. From the present study, on the basis of the pathogenicity test, we suggest the consideration of V. anguillarum, V. alginolyticus, V. harveyi and V. splendidus as primary pathogenic species for gilt-head sea bream.