Sarotherodon niloticus with average weight of 28.42 ± 1.87g were immunized with formalin-killed Edwardsiella tarda using the hyperosmotic infiltration method. Test fish maintained in 30 l aquaria were grouped into four treatments. Group 1 and 2 were exposed to a single hyperosmotic treatment on day 0. Group 1 was bled on day 14 and group 2 was bled on day 28. Group 3 was given hyperosmotic treatments twice: on day 0 and day 14 and bled on day 28. Group 4 was an untreated control bled on day 28. All sera were analyzed for agglutinating antibody titer against E. tarda flagellar and somatic antigens. Results showed that flagellar and somatic agglutinin titers in all treatments were not statistically significant. Likewise, infection experiments where test fish were challenged with intraperitoneal injection of the test bacterium showed that the vaccination experiment did not effectively protect the test fish from infection by Edwardsiella tarda.