Development and efficacy of novobiocin and rifampicin-resistant Aeromonas hydrophila as novel vaccines in channel catfish and Nile tilapia

► Three novel attenuated A. hydrophila vaccines were developed through selection for resistance to both novobiocin and rifampicin. ► Vaccination of channel catfish with the mutants offered 86-100% protection against their virulent parents at 14 days post vaccination (dpv). ► Vaccination of Nile tilapia with the mutants offered 100% protection against their virulent parents at 14, 28, and 56 dpv. ► The three attenuated vaccines might be used to protect channel catfish and Nile tilapia against A. hydrophila.