A DNA vaccine for inducing protective immunity against pseudotuberculosis in fish is provided. The DNA vaccine comprises, as the active ingredient, a DNA comprising a nucleotide sequence encoding an immunogenic polypeptide against Photobacterium damselae subsp. Piscicida, or an expression vector comprising the DNA.本發明提供一種用以誘導針對類結節症之防禦免疫的魚類用DNA疫苗。其係包含:包含編碼針對發光桿菌(Photobacterium damselae subsp.piscicida)之免疫原性多肽的核苷酸序列之DNA、或包含前述DNA之表現載體作為有效成分。