Variation In The Serum Antibody Responses To Environmental Bacteria In Natural Populations Of The Red Drum, Sciaenops ocellatus     Karen G. Burnett1, Mark R. Evans1, Sara-Jane Larsen1, and George H.M. Riekerk2   1Grice Marine Laboratory, University of Charleston, Charleston, SC; 2Marine Resources Research Institute, SC Department of Natural Resources, Charleston, SC     The kinetics, magnitude, specificity and duration of antibody responses in teleost fish have been described most extensively in captive populations.  Such studies may be complicated by factors associated with captivity, such as stress and limited genetic diversity.  To begin evaluating the relevance of an intact immune system to natural populations of a marine teleost, we measured the serum antibody responses of feral red drum against bacteria indigenous to their brackish water environment.  Tag and release studies indicated that each of the five sampling areas in this study had a resident, relatively immobile, population of red drum.  Fish were captured by trammel net, stop net or hook-and-line.  On each collection date, bacteria associated with the fish were sampled immediately and cultured from a mucosal swab.  Biochemical assessment of 74 isolates selected at random from the mucosal cultures assured the heterogeneity of these indigenous bacteria.  Captured fish were examined in the field for general health and the presence of external lesions.  Ages were determined from physical measurements and confirmed by scale annuli.  After blood samples were taken, animals were released to the wild.  As measured by ELISA, individual red drum sera displayed distinctive patterns of antibody response against bacteria isolated from their own habitat.  The percentage of animals with positive responses against bacteria increased with age and water temperature.  When anti-bacterial responses were compared among all five-study populations, striking differences were noted.  These differences did not appear to correlate with the age or general health of the animals, water temperatures, or the density of culturable bacteria of surface waters or adherent to fish scales.  Two locations, Winyah Bay and Plum Island, that had the lowest percentages of non-responsive red drum, also had the highest load of sediment contaminants.  These observations suggest that low anti-bacterial responses may be result from the immunotoxic effects of anthropogenic stressors.  Alternatively, the reproductive and natural history of red drum may support sufficient genetic difference among the populations to explain the stark contrast in antibody responses.  Additional studies are required to test these alternative hypotheses.