In order to understand the mechanism of development of IgM gene expression and its antibody transfer between generations in yellow catfish,Pelteobagrus fulvidraco,IgM gene transcription change and its antibody level in ovary,eggs,embryos,and larvas of P.fulvidraco were investigated by using the Real-time PCR and ELISA techniques.Results were as follows:IgM mRNA not detected in 3-7 d larvae was found in 14 d larvae.Immuning mother fish by bacteria did not influence IgM mRNA expression level in their larvae.IgM antibody in P.fulvidraco exsited in eggs,embryos,and all early phases of larvae.These antibody expression level continued to decline and reached the lowest level in 9 d larvae(which is 0.31 times of eggs'),and began to increase in 14 d larvae(which is 1.6 times of 9 d larvae's).Immuning mother fish by bacteria was able to significantly improve IgM antibody expression levels,which respectively increased to 2,3 times and 1.8 times in eggs and 9 d larvae of P.fulvidraco.These studies indicate that IgM gene expression of P.fulvidraco between generations is discontinuity,while its antibody expression is continous.The IgM antibody in early phases of larvae is from their mother fish.Immunizing may significantly improve antibody level of embryo and larvae.