Dietary therapeutic dose of oxytetracycline negatively influences the antioxidant capacity and immune-related genes expression in Nile tilapia Oreochromis niloticus (L.)

Effects of the dietary therapeutic dose of oxytetracycline (OTC) at 80 mg/kg biomass/day for consecutive 10 days on the behaviour, feed intake, mortality, residue accumulation and depletion, antioxidant capacity and immunerelated genes expression in juvenile Nile tilapia Oreochromis niloticus were evaluated. OTC-dosing caused mortalities, reduced feed intake, and biomass reduction at 24.5-28.5 degrees C. OTC residues recorded on day 10 (161.40 +/- 11.10 ng/g) were within the maximum residue limits of the Codex Alimentarius. The withdrawal period was 7 days as per the European Commission's regulation. Traces of residues were present even on day 42 post-OTC-dosing. Dietary OTC reduced the antioxidant capacity of the liver and muscle tissues and down-regulated the expression of tumour necrosis factor-alpha, interleukin-1 beta, and heat shock protein-70 genes in the liver significantly during the dosing period. The data generated on the biosafety of OTC-dosing may offer inputs for the development of management strategies in maintaining fish health and food safety.

Automated summary

The study found that the dietary therapeutic dose of oxytetracycline in juvenile Nile tilapia could lead to mortality, reduced feed intake, biomass reduction, and negative effects on antioxidant capacity and immune-related gene expression. Residues were within the maximum limits set by Codex Alimentarius, with trace amounts still present even after the withdrawal period.