PATTERNS OF IMMUNE-RESPONSE TO ENVIRONMENTAL BACTERIA IN NATURAL-POPULATIONS OF THE RED DRUM, SCIAENOPS-OCELLATUS (LINNAEUS)

The mechanisms by which natural populations of teleost fish resist inf ection in spite of the wide variety of microorganisms in their environ ment are poorly understood. To begin evaluating the relevance of an in tact immune system to natural populations of a marine teleost, we moni tored age and seasonal patterns of serum antibody responses of feral r ed drum (Sciaenops ocellatus, (Linnaeus)) against bacteria indigenous to their brackish water environment. Among the three populations which were most extensively studied, the percentage of red drum within a na tural population which exhibited serum antibody responses against indi genous bacteria increased with the age of the animals. In red drum fro m two of the three sites, antibody responses were highest in seasons w here water temperatures were highest, but this pattern was difficult t o separate from age-related effects. When anti-bacterial responses wer e 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 bacteria den sities of surface waters and adherent to fish scales. Two locations, W inyah Bay and Plum Island, which had the lowest percentage of non-resp onsive red drum, also had the greatest load of sediment contaminants, suggesting that low anti-bacterial responses may correlate with the le vel of anthropogenic stress. Future studies are being designed to asse ss whether the lack of anti-bacterial antibodies, as measured in this assay, also correlates with decreased antibody responses against indig enous fish pathogens and with an increased susceptibility to opportuni stic infection.