A DNA vaccine for fish, characterized by - imparting immunity against pseudotuberculosis caused by Photobacterium damselae subsp. piscicida; - comprising, as an active ingredient, a DNA comprising a nucleotide sequence encoding an immunogenic polypeptide against Photobacterium damselae subsp. piscicida; a DNA comprising a nucleotide sequence prepared by modifying the sequence based on a codon usage in Japanese flounder; or an expression vector comprising the DNA, wherein the immunogenic polypeptide is a polypeptide consisting of the amino acid sequence of SEQ ID NO: 2; a polypeptide comprising the amino acid sequence of SEQ ID NO: 2; or a homologous polypeptide with immunogenicity against Photobacterium damselae subsp. piscicida, comprising an amino acid sequence having a 90% identity or more with the amino acid sequence of SEQ ID NO: 2; or an immunogenic partial fragment of any one of the polypeptides to, whereby the length of the partial fragment is not limited, so long as a polypeptide encoded by the partial nucleotide sequence can induce immunity, including humoral immunity and cellular immunity, against Photobacterium damselae subsp. piscicida in the living body. - imparting immunity against pseudotuberculosis caused by Photobacterium damselae subsp. piscicida; - comprising, as an active ingredient, a DNA comprising a nucleotide sequence encoding an immunogenic polypeptide against Photobacterium damselae subsp. piscicida; a DNA comprising a nucleotide sequence prepared by modifying the sequence based on a codon usage in Japanese flounder; or an expression vector comprising the DNA, wherein the immunogenic polypeptide is a polypeptide consisting of the amino acid sequence of SEQ ID NO: 2; a polypeptide comprising the amino acid sequence of SEQ ID NO: 2; or a homologous polypeptide with immunogenicity against Photobacterium damselae subsp. piscicida, comprising an amino acid sequence having a 90% identity or more with the amino acid sequence of SEQ ID NO: 2; or an immunogenic partial fragment of any one of the polypeptides to, whereby the length of the partial fragment is not limited, so long as a polypeptide encoded by the partial nucleotide sequence can induce immunity, including humoral immunity and cellular immunity, against Photobacterium damselae subsp. piscicida in the living body. a DNA comprising a nucleotide sequence encoding an immunogenic polypeptide against Photobacterium damselae subsp. piscicida; a DNA comprising a nucleotide sequence prepared by modifying the sequence based on a codon usage in Japanese flounder; or an expression vector comprising the DNA, a polypeptide consisting of the amino acid sequence of SEQ ID NO: 2; a polypeptide comprising the amino acid sequence of SEQ ID NO: 2; or a homologous polypeptide with immunogenicity against Photobacterium damselae subsp. piscicida, comprising an amino acid sequence having a 90% identity or more with the amino acid sequence of SEQ ID NO: 2; or an immunogenic partial fragment of any one of the polypeptides to, whereby the length of the partial fragment is not limited, so long as a polypeptide encoded by the partial nucleotide sequence can induce immunity, including humoral immunity and cellular immunity, against Photobacterium damselae subsp. piscicida in the living body.