Plasma and tissue distribution of dietary oxolinic acid and its influence on the biological responses of Nile tilapia Oreochromis niloticus

Intensive aquaculture requires effective strategies for managing bacterial diseases and regulating the use of antibiotics. This study examined the effects of oral oxolinic acid (OA) administration for 7 days at 12 mg and 36 mg/kg biomass/day in Oreochromis niloticus, and compared the treatment groups with the control. Mortalities in the range of 3.33 - 8.33% during OA administration were noted. The OA-fed fish's haemogram, haematological indices, erythrocytes, and plasma biochemical parameters related to general and oxidative stress, ionic balance, and functioning of vital organs exhibited significant changes. The OA residues peaked in the muscle, liver, kidney, and plasma on day 7 of administration. The residues persisted even after 35 days of dose suspension in the muscle of both groups. The projected withdrawal period of OA with 95% confidence and tolerance limits was 4 days. Residues were depleted more rapidly in the liver, plasma, and kidneys. Although recovery was observed, none of the measured parameters returned to normal on day 35 post-dosing. Although safe, these findings suggest that the recommended dose of OA may induce reversible biological responses in fish and should be used in aquaculture with appropriate caution.