Cryptocaryon irritans, a marine parasitic protozoan, poses a significant threat to marine teleosts, including golden pompano (Trachinotus ovatus) species. Studies show that T. ovatus can develop specific immunity following C. irritans exposure. However, the precise mechanisms underlying the immune response remain unclear. Therefore, this study aims to investigate the effects of an immunization protocol in pompano, involving their exposure to non-lethal doses of theronts, achieving a 44.6 % reduction in infection rates compared to the controls. Parasite-specific Immunoglobulin M (IgM) levels increased in the serum, mucus, and explant supernatants of immunized pompano, with significantly enhanced IgM-positive signals in the skin and spleen, indicating systemic and mucosal immunity activation. Furthermore, the developed immunity against C. irritans in immunized pompano was compromised by injecting rabbit polyclonal antibodies (pAbs) against pompano IgM, resulting in decreased parasite-specific IgM levels, reduced IgM-positive signal, and higher tomont counts. In conclusion, this study demonstrates the induction of IgM immune response in pompano following C. irritans exposure and underscores the critical role of IgM in defense against this pathogen, offering a theoretical foundation for future vaccine development.