Serum lysozyme attivity was measured using a modified turbidimetric microtither plate technique according to Ellis [32]. Briefly, a standard suspension of 0.15 mg/ml micrococcuc lysodeikticus (Sigma) was prepared in a 66 mM phosphate buffer (pH 6.0). Flounder serum (50 ) was added to 1 ml of bacterial suspension, and the decrease in absorbance was recorded at 0.5 and 4.5 min intervals at 450 nm in a spectrophotometer (SHIMADZUUV-1600PC). One unit of lysozyme activity was defined as reduction in absorbance of 0.001/min.