We initiated the first cage culture of the Mediterranean horse mackerel (Trachurus mediterraneus) in the Black Sea. The wild fish was captured by purse seine and transferred into sea cages. Fish were fed by sea bass feed during grow out period, but fish mortalities were observed. However, the causes of mortalities were unknown. Therefore, cultured Mediterranean horse mackerel have been sampled monthly for two years to determine possible parasitic and bacterial agents. During the study, no parasite was found while several Gram negative bacterial species including Aeromonas hydrophila, Chryseobacterium indologenes, Vibrio vulnificus, Bulkholderia cepacia, Photobacterium damselae damselae and Vibrio alginolyticus were isolated from cultured fish. Antibiotic resistance analyses showed that more than 50% of the bacteria were resistant to streptomycin, sulfamethoxazole, gentamycin, cephalothin, and ampicillin while they were very sensitive to florfenicol and chloramphenicol. The most prevalent resistance genes were found to be beta-lactam (bla(TEM-OT3-4)) and Tetracycline (tetB). This is the first study reporting isolation and antibiotic sensitivities of bacterial species in horse mackerel, which is expected to be a valuable source in predicting possible disease problems in horse mackerel aquaculture. (c) 2013 Elsevier B.V. All rights reserved.