Specific antibody secreting cells (ASC) play an important role in the immune response. In this study, to detect changes in specific ASCs in the Nile tilapia (Oreochromis niloticus) in response to exogenous stimuli, the number of ASCs in the head kidney, peripheral blood, and spleen of this fish after immunization with human IgG was detected by enzyme-linked immunospot assay (ELISPOT). The results showed that ASCs could be detected in the head kidney on day 1 after the first immunization, while ASC could be detected in the peripheral blood and spleen on day 3. The number of ASCs in the head kidney, peripheral blood, and spleen all reached their peak on day 12. While the number of ASCs in the kidney and peripheral blood was significantly reduced, that in the spleen was not significantly reduced. Subsequently, ASCs could be detected in the head kidney, peripheral blood, and spleen on day 1 after the second immunization, with the number of ASCs reaching their peak on day 9, earlier than the first immunization. In both the first and second immunizations, the number of ASCs in the head kidney tissue was the highest among the three tissues. Using enzyme linked immunosorbent assay (ELISA) to detect the antibody levels in serum after the first and second immunizations, the change trend was found to be the same as that of the ASCs. These results indicate that the Nile tilapia developed immune memory after the first immunization and produced more ASCs and antibodies during the second immunization. Furthermore, the head kidney was identified as the main source of ASCs. These findings provide an important scientific basis for the study of immune memory in fish.