A group consisting of 20 individuals of Japanese flounder Paralichthys olivaceus was reared for 178 days, during which edwardsiellosis occurred. Monitoring of immunological (phagocytic rate, NBT reduction and potential killing activity of blood phagocytes and lysozyme activity in the plasma) and hematological (protein concentration and glucose concentration in the plasma) parameters were carried out throughout the period, using the blood periodically collected from each fish. Relative standard deviation (SD/average) values of most of the parameters were expanded several weeks before mortality started. The expansion of these values is thought to be caused by increased physiological differences between normal and infected fish in the group. The variance value of these parameters is suggested to be useful to recognize a sign of outbreaks of infectious diseases.
