The present invention discloses novel proteins, e.g., antigens, from Piscirickettsia salmonis. The present invention further discloses nucleic acids that encode these proteins. The present invention also discloses the use of the proteins, e.g., antigens, and nucleic acids to prepare vaccines against salmonid rickettsial septicemia (SRS). The present invention also discloses vaccines that can be used to protect fish from Piscirickettsia salmonis, as well as other pathogens. In addition, the present invention discloses methods of using the vaccines of the present invention to protect fish from SRS as well as from other pathogenic diseases.