We evaluated the effects of water temperature on the kinetics of skin mucus antibody in the flounder sing an indirect enzyme-linked immunosorbent assay (ELISA). The fish were held at 9 and given an intraperitoneal injection of inactivated lymphocystis disease virus (LCDV). The optical density (OD) of mucus antibody peaked 9 and 7 weeks after treatment in the groups held at 9 during the 5th week. The OD was lower in fish held at 26) in the 5th week. We collected a sample of skin mucus from fish with the highest OD and extracted mucus Ig by ammonium sulfate precipitation. The mucus proteins from all four treatment groups yielded bands at 72 kD and 26 kD. Western blotting analysis revealed that the monoclonal antibody against serum Ig heavy chain could only recognize the 72 kD protein, which represents the heavy chain of skin mucus Ig. In conclusion, the most pronounced immune response was measured in fish that were maintained at their optimal temperature (21