Fluoroquinolones and tetracyclines as growth factors in aquaculture: Increase of biometrical parameters versus emergence of resistant bacteria and residues in meat

Antibiotics can be used as growth promoters for fishes in aquaculture. However, its use in animal production induced an increase in the emergence of resistant microorganisms. Piaractus mesopotamicus is the second most produced fish species in Argentina. The aim of this work was to evaluate the effect of the administration of subtherapeutic doses of oxytetracycline and enrofloxacin over biometrical parameters, the increase of resistant microorganisms in the intestinal microbiota and the presence of antibiotic residues in meat of P. mesopotamicus. 3 months old animals were fed twice a day for 120 days. Commercial balanced feed was added with either oxytetracycline (O), enrofloxacin (E) or water (C). Biometrical parameters, intestinal content (IC) and muscle samples were obtained every 30 days. IC samples were inoculated in plates with and without antibiotics while muscle samples were submitted to a microbiological method to find antibiotic residues. Treatment O maintained survival at 100%, increased mean weight and standard length and was not detected in muscle samples. However, it showed the highest increments in the number of resistant microorganisms. These results indicate that the use of subtherapeutic doses of oxytetracycline for prolonged periods induces increments in biometrical parameters leaving no residues in meat, but also promotes the development of resistant microorganisms when compared with the control group.