Serum and Tissue Kinetics of Oxolinic Acid in Black Rockfish (Sebastes schlegelii) Following a Single Oral Administration at Two Temperatures

The objective of this study was to investigate the pharmacokinetic (PK) properties of oxolinic acid (OA) in black rockfish (Sebastes schlegelii) following a single oral administration of 30 mg/kg at 13°C and 22°C. Serum and tissue (muscle, liver and kidney) samples were collected at pre-determined time points and analysed using high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). The results demonstrated that temperature significantly influenced the PK parameters of OA. The terminal half-life (t_1/2λz) was prolonged at 22°C across all tissues, while the total body clearance (CL/F) was reduced, suggesting a slower drug elimination at higher temperatures. The peak concentration (C_max) and the area under the concentration-time curve (AUC) values increased with temperature, indicating enhanced systemic exposure at 22°C. The volume of distribution (Vz/F) decreased from 13°C to 22°C, indicating reduced tissue distribution of OA at the higher temperature. PK/pharmacodynamic (PK/PD) analysis revealed that a single oral dose of 30 mg/kg was insufficient to achieve optimal antibacterial efficacy, implying that higher doses may be necessary. These findings highlight the necessity of temperature-adjusted dosing strategies for OA treatment in black rockfish aquaculture to optimise therapeutic efficacy while minimising antimicrobial resistance risks.