diluted with 2.6% NaCl by a twofold method in a multiwall-plate. A suspension of V. harveyi was added into the diluted serum and incubated at room temperature for 3 hrsbefore enumerating the number of bacteria by a spread plate technique on thiosulfate citrate bile sucrose agar (TCBS). The results were recorded as the lowest dilution that killed 50% of the V.harveyi compared to the control.