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Pangasianodon hypophthalmus is one of the most important aquaculture species in Southeast Asia, with a significant contribution to the world fish basket. Like other crops, the striped catfish suffers from bacterial diseases that demand the use of antibiotics. The present study has evaluated the safety of oxytetracycline, one of the approved and commonly used antibiotics, in this species. Juvenile stages of the fish (31.16 ± 1.03 g) were administered with the antibiotic in feed at the dose rate of 80–800 mg kg−1 body weight daily for 30 days, followed by 10 days of withdrawal observation. Fish health was assessed by the study of behaviour and feed intake, haematology, blood biochemistry, and histopathology. Results showed that up to 30 days of antibiotic treatment resulted in no significant toxic effects in terms of behaviour and fish mortality. However, fish suffered from reduced feed intake and hepatotoxicity evidenced by proliferative and degenerative changes of hepatocytes, and increase in AST and ALT enzyme activities, especially in 400–800 mg kg−1 doses which, however, recovered after withdrawal of the drug. Although few fish died from a bacterial infection at the lowest concentration of the drug used, fish were able to mount adaptive physiological responses best at 80 mg kg−1 fish dosage. The study establishes that in‐feed administration of the antibiotic oxytetracycline @ 80 mg kg−1 fish biomass is safe for therapeutic use in P. hypophthalmus. [ABSTRACT FROM AUTHOR]