Technical Abstract: Aquaflor® (florfenicol, 50% type A medicated article) is a relatively new antibiotic used in U.S. aquaculture and has been widely accepted as a safe and effective therapeutant. Some peer-reviewed studies have suggested that 15 mg FFC/kg BW/d for 10 d can control mortality to a greater extent than 10 mg FFC/kg BW/d for 10 d. This study evaluated the safety of Aquaflor® to sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) when administered in feed at 15 (1× the maximum proposed therapeutic dose), 45 (3×), or 75 (5×) mg florfenicol/kg BW/d for 20 d (2× the currently approved 10-d treatment duration). The medicated feed was top-coated with Aquaflor® and fed at 2% BW/d divided equally between the morning and afternoon feeding. Juvenile sunshine bass (13.6 ± 1.6 g, mean ± SD) were stocked into 100-L flow-through tanks at 20 fish/tank. Diets were randomly assigned to 3 replicate tanks per treatment; three additional non-study tanks were fed control diets and weighed weekly to calculate proper feeding quantities. Throughout the trial, water quality was maintained within ranges suitable for sunshine bass culture, fish behavior appeared normal, and all feed was readily and rapidly consumed. There were no mortalities and fish health evaluations revealed no chronic toxicity patterns. None of the histopathologies distinctive to the use of Aquaflor® were observed. In conclusion, there is an adequate margin of safety associated with administering Aquaflor®-medicated feed to fingerling sunshine bass at the proposed therapeutic treatment regimen of 15 mg florfenicol/kg BW/d for 10 d.