Solvent extraction of Omega-3 polyunsaturated fatty acids (PUPA) ethyl esters (Et) from 18/I2EE fish oil was performed with an aqueous silver nitrate solution in a mini-fluidic reactor framework. The resulting extraction was compared within conventional stirred-tank reactors, with practical extraction yields of EPA-Et and DHA-Et approaching 60 to 70 wt %. Equilibrium was reached in less than 36 s at 10 degrees C, despite stratified flow being observed rather than previously reported slug-flow profiles in idealized fluid pairs at these scales. The deviation in flow pattern was attributed to a measured order of magnitude reduction in the interfacial tension between fish oils and AgNO3 solution relative to idealized solvent mixtures using hexane/heptane as a carrier for purified EPA/DHA. The impact of solvent addition to fish oils on interfacial tension with silver nitrate solutions was subsequently explored through spinning drop tensiometry, suggesting that the heterogeneous nature of raw fish oils will yield significantly different flow patterns than previously considered in extraction studies utilizing AgNO3 solutions. These results are applicable both to mini-fluidic systems and for the approximation of interfacial tension in fish oil/organic/aqueous extraction systems.