Impact of graded doses of enrofloxacin on the safety and biological responses of Nile tilapia Oreochromis niloticus.

The cultivation of tilapias, the third most farmed fish group globally, has been rapidly growing, especially in Southeast Asia. This surge in tilapia farming intensification has led to increased use of antibiotics to control bacterial diseases. This study investigated the safety implications of administering graded doses of enrofloxacin (ENF) at 0 (control), 10, 30, 50 and 100 mg/kg biomass/day orally to Oreochromis niloticus. The 43-day study comprised 7 days of pre-dosing, 15 days of ENF-dosing, and a 21-day recovery period with a periodical assessment of the biological responses of fish. The results revealed that the overdosed groups experienced up to 21% reduction in feed consumption, 11% mortalities, and adverse impacts on hematology, including a decrease in erythrocytes, and monocytes and an increase in leukocytes, thrombocytes, lymphocytes, and neutrophils. Haematological indices like mean corpuscular volume and mean corpuscular hemoglobin decreased, while mean corpuscular hemoglobin concentration increased. The plasma biochemical parameters including glucose and liver and kidney enzymes unveiled a significant dose- and time-dependent increase, while calcium and chloride levels decreased. Erythrocytes displayed several erythrocyte cellular and nuclear abnormalities. The frequency of micronucleus increased with dose and time, suggesting potential genotoxicity of ENF. Additionally, a dose-dependent increase in residues in the tissues with the highest accumulation in muscle was documented. Nevertheless, the recovery of the measured parameters upon dose termination indicated that the ENF-induced alterations are reversible. The study affirmed the safety of ENF at the recommended dose (10 mg) in O. niloticus and their adoptive responses to higher doses.