The concern surrounding animal antibiotics focuses on meat and poultry production, but a new study suggests we should also be paying attention to fish. Researchers at Arizona State University investigated 47 antibiotics in U.S.-purchased shrimp, salmon, catfish, trout, tilapia and swai originating from 11 different countries. Their findings, published in the Journal of Hazardous Materials, identified five antibiotics detected in shrimp, salmon, tilapia and trout. Oxytetracycline was the most commonly detected antibiotic compound, and it was found in farmed fish and wild shrimp. The researchers also found 4-epioxytetracycline, sulfadimethoxine, and ormetoprim in certain species and virginiamycin in farmed salmon marketed as antibiotic-free. Lead author Hansa Done, a Ph.D. candidate at ASU’s Center for Environmental Security, told Time.com that antibiotics are added to the water in fish farms to treat and prevent disease or are directly injected into fish, but that they are not used for growth promotion. The antibiotic levels detected in the study were within legal limits, and the researchers report low risk of drug exposure from seafood consumption, but even the low levels can promote antibiotic resistance. The authors add that publications reporting antibiotic resistance in aquaculture have increased eight-fold over three decades.