The variation trend of IgM titers in serum could effectively reflect the variation of IgM expression level and the potency of rSip injection to elicit fish immune response to some degree, and the two variable trends of IgM titers and IgM expression level (EF1A and ACTB together as the reference genes) were similar in practice, which indicated that the two recommended genes EF1A and ACTB were suitable as reference genes for normalizing IgM expression during vaccination and infection. The gene discussed is CD40LG; the disease is infection.