A Comparison Of Lymphocyte Separation Techniques Used For Peripheral Blood Lymphocytes In Fish     Kristina E. Howard, Virginia Buechner-Maxwell, Stephen A. Smith   Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0442, USA     A comparison was made of lymphocyte separation techniques previously employed in other species of fish and birds to determine if any were superior for the isolation of peripheral blood lymphocytes. Modifications were made to techniques previously described and tested on tilapia (Oreochromis niloticus), a teleost fish.  The use of a 59% Percoll density gradient provided high levels of lymphocyte yield and purity with good mitogenic response and cell viability.  A slow speed centrifugation technique also provided good rates of recovery and purity, but was not as consistent as the Percoll density gradient.  These studies show that sufficient cells can be obtained from tilapian peripheral blood to conduct non-lethal immunologic assays.