Depletion study and estimation of withdrawal periods for florfenicol and florfenicol amine in pacu (Piaractus mesopotamicus)

The intensive production of farmed fish is at a global all-time high, and the control of bacteria proliferation in fish farms requires the frequent use of antimicrobials. This practice raises important environmental concerns related to the emergence of antimicrobial-resistant bacteria strains. Only a few antimicrobial drugs have been approved for use in aquaculture, one of which is florfenicol. This work studies the depletion and withdrawal period of florfenicol and its main metabolite, florfenicol amine, in pacu (Piaractus mesopotamicus), a neotropical characin widely farmed in the southern hemisphere. Juvenile pacu (average weight of 724g) were stocked in a closed-loop laboratory system with controlled water temperature (25.8 degrees C), and were fed for 10 consecutive days with a diet containing an intended dose of 10mg/florfenicol per kg bw. Muscle and skin tissues were collected at 1, 3, 6, 8, 10, 12 and 16days post-treatment, and florfenicol and florfenicol amine were quantified using a validated ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method. The limits of quantitation for florfenicol and florfenicol amine were 10ng/g in muscle and 50ng/g in skin. Considering a maximum residue limit of 1000ng/g for the sum of florfenicol and florfenicol amine in muscle with skin in natural proportions a withdrawal period of 5days (water temperature 25.8 degrees C) or 129 degree days was calculated on the basis of the upper limit of the one-sided 95% confidence interval for the 99(th) percentile derived from the residue depletion study.