Fate of oxytetracycline in a fresh water fish farm: influence of effluent treatment systems

The fate of orally administered oxytetracycline in a fresh-water hatchery was investigated using high-performance liquid chromatography. A filter of nominal porosity 50 μm in the farm effluent was capable of at least a 500-650-fold concentration of the oxytetracycline into the filter retentate flow. No oxytetracycline was detected in the filtered farm effluent (limit of detection 0.02 μg·ml^-1). Analysis of hourly samples of the retentate taken over a 24-hour period allowed an estimate of the daily amount of oxytetracycline retained by the filter. This estimate (1250 g) was of the same order as the amount of oxytetracycline used on the farm (904 g on the day of sampling and 1104 g on the preceding day). Thus the quasi-totality of the input oxytetracycline was removed from the farm effluent by the filter. A sedimentation trap on the filter retentate flow removed oxytetracycline from this flow at a variable and lower (12-92%) efficiency. It is argued that correct design of effluent treatment systems could significantly reduce the environmental impact of land-based fish farms.