Protein concentrations in three aquacultural recirculation systems and protein removal by foam fractionation were investigated. The results revealed that protein concentrations ranged from less than 1 to 127 mg/L in the systems tested and averaged about 4% of the concentrations of total volatile solids. These proteins were partially (about 11%) removed by foam fractionation processes, and the removal rate declined as treatment time progressed. Protein concentrations on the bubble surfaces during foam fractionation could be approximated by their linear relationship to protein concentrations in the bulk solution.