Evaluation of biosafety of oral oxolinic acid administration to Nile tilapia Oreochromis niloticus (L.) juveniles
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Date
2022
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West Bengal University of Animal & Fishery Sciences, Kolkata
Abstract
Oxolinic acid (OA) is one of the broad-spectrum quinolones that is a critically important medicine for humans and is used as a second-line treatment in aquaculture at 12 mg/kg biomass/day for 7 consecutive days. The present study was executed to evaluate the biosafety of OA and to determine its efficacy against Aeromonas hydrophila infection in Nile tilapia Oreochromis niloticus juveniles. The study also evaluated the biochemical, histopathological and haematological alterations in O. niloticus when fed the OA feed. The biosafety experiments were carried out at 0-10 times the therapeutic dose (12 mg) for 21 days. A significant dose-dependent reduction in feed intake and biomass and an increase in mortalities was recorded. Dietary OA administration caused a dose-dependent effect on fish erythrocyte morphology and haematological parameters. A significant increase in plasma glucose, creatinine, alkaline phosphatase, alanine transaminase and aspartate transaminase was documented during the dosing period. On the other hand, the plasma calcium and chloride levels decreased significantly. The gills, kidneys, liver, spleen, and intestine showed mild to marked histopathological changes, indicating the possible toxic effects of OA on different organs of fish. The majority of the alterations, however, recovered upon cessation of OA-dosing. The edible tissue residues, as analyzed by LC-MS/MS, peaked on day 21 of OA-dosing and decreased upon cessation of OA-dosing in all the dosing groups. The residue levels of OA in the muscle tissue of the therapeutic dose group were well within the maximum residue limit (MRL) set by the European Medicines Evaluation Agency (EMEA) and Food Safety and Standards Authority of India (FSSAI). Further, the efficacy of OA was evaluated by challenging O. niloticus juveniles with A. hydrophila intramuscularly and subsequently treated with medicated OA feed for 7 consecutive days at 12 mg/kg biomass/day. The OA treatment gave better results in terms of reducing the clinical biochemical parameters and recovery against A. hydrophila infection compared to the untreated group. The rate of wound healing was also faster in the OA-treated group compared to the untreated group, wherein the wounds healed completely within 12 days of post-injection. Therefore, the efficacy of OA against A. hydrophila infections in fish was established. Although the current study hinted at the safety and tolerability of OA in O. niloticus juveniles in tropical Indian conditions, care must be exercised for its aquacultural application because of its listing as a critically important medicine for humans.