Abstract: Live-attenuated vaccines against Edwardsiella ictaluri or against Pasteurella piscicida are disclosed. Both vaccines are incapable of reversion to virulence, because both are made by deletion mutations in the aroA gene, the purA gene, or both. These vaccines may be used not only to vaccinate fish against Edwardsiella ictaluri or Pasteurella piscicida, but also to serve as vectors to present antigens from other pathogens to the fish, thereby serving as vaccines against other pathogens as well, with no risk of infection by reversion to the virulent form of the pathogen in which the antigen occurs naturally.