The most used antibiotics in fish farms are oxytetracyline (OTC) and florfenicol (FLO) (Rigos and Troisi, 2005). OTC is a tetracycline broad-spectrum antibiotic with bacteriostatic action produced by Streptomyces spp. fungi, used to treat systemic bacterial infections of fish (Jerbi et al., 2011). FLO is a structural analog of chloramphenicol similar to thiamphenicol,but is more active against some bacteria than chloramphenicol (Cannon et al., 1990).