The most frequent infectious diseases that affect fish are those of bacterial origin. In European sea bass fish farms (Dicentrarchus labrax) are included Vibrio spp., Pasteurella piscicida and Myxobacter spp. In addition to these, it is also possible to find, although lesser frequently, other pathogenic agents such as Pseudomonas spp., Aeromonas spp., Staphylococcus epidermis, Streptococcus spp. and Enterobacter spp. The presence of these micro-organisms in fish farms contributes for a significant decrease in fish production and subsequent loss of profitability in these aquaculture units. The use of antibiotics may therefore be necessary as a prophylactic measure although their systematic utilization leads to the development of strains of antibiotic resistant bacteria. Bearing that in mind, a survey was conducted on the susceptibility of isolated strains of bacteria found in juvenile European sea bass. It was concluded that chloranphenicol and tetracycline are two important antibiotic alternatives for therapy against isolated bacterial agents.