Plasma and muscle pharmacokinetics of danofloxacin were investigated after 10 mg/kg intravenous (IV, caudal vein) and intramuscular (IM, right epaxial muscles) administrations in 168 healthy brown trout (Salmo trutta fario) at 10°C–13°C. High-performance liquid chromatography was used to determine its plasma and muscle concentrations. Pharmacokinetic parameters were analysed with a non-compartmental model. After IV administration, elimination half-life (t 1/2ʎz ), area under the concentration–time curve (AUC 0–∞ ), mean residence time (MRT 0–∞ ), volume of distribution at steady state, total body clearance in plasma and AUC Muscle /AUC Plasma ratio were 22.22 h, 140.66 h*µg/mL, 23.15 h, 2.28 L/kg, 0.07 L/h/kg and 3.79, respectively. After IM administration, t 1/2ʎz , AUC 0–∞ , MRT 0–∞ , peak concentration (C max ), time to reach C max , bioavailability in plasma and AUC Muscle /AUC Plasma ratio were 28.28 h, 84.39 h*µg/mL, 37.31 h, 4.79 µg/mL, 1 h, 59.99% and 8.46, respectively. Danofloxacin exhibited long t 1/2ʎz and good bioavailability after IM administration. Therefore, 10 mg/kg IM administration of danofloxacin in brown trout can provide AUC 0–24 /MIC of > 125 and C max /MIC of > 10 to treat diseases caused by susceptible bacteria with ≤ 0.336 µg/mL MIC.