Cost effective oxygenation equipment design and operation in high density recirculating aquaculture systems (RAS) requires consideration of the effects of RAS component design, water quality, and biological processes on oxygen transfer requirements. A computer model was developed to simulate multi-component gas transfer and biological respiration in a pilot scale recirculating aquaculture system employing an u-tube aerator. Gas transfer and/or biological respiration are modeled for all system components; production tank, multi-tube clarifier, rotating biological contactor and the u-tube. The calibrated model predicted equilibrium oxygen concentrations in the production tank to within ± 1 mg/L in the validation tests. The model was then used to investigate techniques to reduce oxygen transfer costs associated with aquaculture in the RAS located at the Virginia Tech Aquaculture Research Facility. / Master of Science