The compatibility and efficacy of enrofloxacin (Baytril) a newly developed antibiotic belonging to the quinolones, were tested for five ornamental fish species (Herotilapia multispinosa, Pterophyllum scalare, Symphysodon discus, Brachydanio rerio and Melanochromis johanni). The results prove that enrofloxacin has a high tolerance level for ornamental fishes and high efficacy against important bacterial diseases. 30 micrograms/l water over 5 hours are recommended for the treatment of ornamental fishes.