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Summer flounder, Paralichthys dentatus, culture is becoming increasingly popular in the United States because of high market prices and consumer demand. In addition, flounder is a marine fish species that can tolerate a wide range of salinities, allowing for inland intensive fish culture. Oxytetracycline (OTC) is one of two available FDA-approved antibiotics for use in foodfish in the United States. Oxytetracycline was chosen for these studies because it is excreted primarily unchanged through the urine and the absorption, distribution and elimination of this drug may be influenced by environmental and physiological conditions. Four experiments were conducted to investigate: 1) pharmacokinetic parameters of oxytetracycline (50 mg/kg) following intravascular (IV), intraperitoneal (IP), intramuscular (IM) and per os (PO) administration in summer flounder maintained at 28 ppt salinity and 20°C; 2) pharmacokinetic parameters of OTC (50 mg/kg) following IM and PO administration in summer flounder maintained at three different salinity levels of 0 ppt, 15 ppt and 32 ppt and the physiological adjustments summer flounder make to acclimate to environmental salinity; 3) OTC retention times in muscle tissue from summer flounder maintained at three different salinity levels (0 ppt, 15 ppt, 32 ppt) and treated with a single 50 mg/kg OTC dose via IM and PO administration; and 4) pharmacokinetic parameters of OTC (50 mg/kg) following IM and PO administration in clinically healthy and clinically diseased summer flounder maintained at 28 ppt and 20°C. Oxytetracycline plasma concentrations were determined using high performance liquid chromatography (HPLC) and analyzed using a non-compartmental pharmacokinetic model for all routes of drug administration. Statistical comparisons were not made between the different routes of OTC exposure, but results from experiment one indicated that IV administration of OTC resulted in the largest area under the curve (AUC) value (8147.9 µg·h/ml) and the highest maximum plasma concentration (Cmax) of 1173.2 µg/ml OTC at 5 min post-injection. Intramuscular injections of OTC resulted in prolonged total body elimination half-life (T ½) of 301.3 h and high fish-to-fish variability (0.6). Per os administration resulted in low Cmax (0.2 µg/ml OTC) and poor systemic bioavailability (0.2 %). Results from experiment two demonstrated that when OTC is administered IM AUC estimates are significantly (p