The aim of this study was to describe a case of skin lesions with haemorrhaging in a carp (Cyprinus carpio) hatchery farm and to determine effective antibiotic treatments. In the macroscopic examinations of nine carp with haemorrhagic skin lesions, brown or red spotted skin changes of a varying degree were found, along their bodies. No lesions were observed in the internal organs. Pure cultures of Aeromonas hydrophila were isolated from the skin, kidney, heart, and liver of the carp. All of the isolates were found to be susceptible to danofloxacin, enrofloxacin, gentamicin, ciprofloxacin, neomycin, and trimethoprim-sulphamethoxazole and resistant to ampicillin, amoxicillin, amoxicillin/clavulanic acid, oxytetracycline, and streptomycin. Treatment of A. hydrophila infection was carried out by applying trimethoprim-sulphamethoxazole for 3 d at 10 g/ton of pool water.