Thinh H. Nguyen * , & Hue N. D. Truyen

* Correspondence: Nguyen Huu Thinh (email:

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The efficacy of florfenicol for control of mortality associated with Flavobacterium columnare was studied in tilapia. F. columnareT3-8/10 strain used for infection was tested for virulence by bath challenge to tilapia (body weight: BW 14 - 16 g) and antimicrobial sensitivity test. The results showed LD50 of this bacterial strain was 4.8 × 104CFU/mL and it was sensitive to florfenicol. Ex-periment for control mortality caused by the bacterium in tilapia (BW 18 – 20 g) was designed with four treatments including neg-ative control (unifected fish), positive control, NT10 and NT15 (infected with LD50). Just after infection, fish in positive control, NT10 and NT15 treatments were treated with florfenicol at doses of 0, 10 and 15 mg/kg BW/day for 10 days, respectively, by feed-ing fish with medicated feed. Mortality of fish in positive control treatment after 14 days of infection was 54.0 ± 5.47% and statisti-cally different in comparison with those in negative control, NT10 and NT15 treatments were 0.0, 3.0 ± 4.72 and 2.60 ± 2.51%, re-spectively (P < 0.05). Fish in NT10 and NT15 treatments were sampled for testing florfenicol residue in the flesh at day 1, 16, 20 and 24 after treatment. The results showed florfenicol residue levels in the flesh of sampled fish at all testing timepoints were sig-nificantly lower in comparision with the safe concentration lower than 1000 ppb regulated by the Ministry of Agriculture and Rural Development of Vietnam.

Keywords: Flavobacterium columnare, Florfenicol, Tilapia

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