Abstract

The rational use of antimicrobials in aquaculture requires rigorous clinical safety assessments to ensure fish health and to minimize toxicological risks associated with drug administration. This study evaluated the clinical safety of orally administered antimicrobials incorporated into feed, representing different pharmacological classes, in Nile tilapia (Oreochromis niloticus). Three bioassays were conducted for sulfadimethoxine combined with ormetoprim (SDM–OMP, 50, 100, and 200 mg·kg−1, at a fixed 5:1 SDM:OMP ratio), spiramycin (SPM, 40, 80, and 160 mg·kg−1), and phenoxymethylpenicillin potassium (PMP, 10, 20, and 40 mg·kg−1), including control and treated groups at different dose levels, followed by a drug-free recovery period. The assessment integrated hematological parameters, serum biochemical analyses, and histopathological evaluations of the liver, kidney, and spleen. Exposure to the antimicrobials resulted only in mild, transient, and reversible physiological alterations, with no evidence of clinically relevant toxicity or structural lesions in the analyzed organs. Collectively, these findings demonstrate that SDM–OMP, SPM, and PMP exhibit a favorable clinical safety profile in Nile tilapia, even at doses up to four times the recommended therapeutic level, supporting their responsible use in aquaculture under controlled conditions.

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