Oxytetracycline residues in cultivated marine shrimp (Litopenaeus vannamei Boone, 1931) (Crustacea, Decapoda) submitted to antibiotic treatment

Shrimp culture is a very important economic activity in the world and the fastest growing industry in Northeastern Brazil. Problems with diseases are common in aquaculture and at the least seven species of Vibrio bacteria have been documented infecting shrimps during different culture stages. Oxytetracycline (OTC) has been widely used against these pathogens. In the present study the distribution and residue depletion of OTC in Litopenaeus vannamei tissue were evaluated after 14 days of exposure to medicated feed containing 4 g/kg. Two trials were conducted: in indoor tanks under laboratory-controlled conditions and in cages installed in an outdoor commercial shrimp grow-out pond. Medicated animals were sampled periodically during the treatment period and thereafter. The tissue levels of OTC were measured by high-performance liquid chromatography (HPLC). Although conditions were similar for both treatments, OTC peak concentrations differed. After 7 and 12 days of exposure to OTC, the maximum tissue residue levels were 17.21 and 4.38 mu g/g for shrimp reared in the laboratory and in the pond, respectively. The mean OTC tissue residue concentration observed for both experimental environments is within the limits of the minimum inhibitory concentration (MIC) determined for vibriosis treatment. Drug residue levels dropped quickly during the first 72 It after treatment termination, then slowly and steadily until a residue level of 0.1 mu g/g, considered a safe limit by the European Community requirements, was attained at day 16 of OTC withdrawal. After 25 days of OTC withdrawal no drug residues could be detected. However, a longer withdrawal period is recommended to ensure complete drug depletion. (c) 2005 Elsevier B.V All rights reserved.