Common carp, one of the most cultured fish species worldwide, is threatened by many diseases. In this research we developed and tested vaccines against two important carp viruses and besides the traditional injection-vaccination, we explored possibilities for oral (stress-free) vaccination. For one of the viruses we successfully developed a DNA vaccine that induced full protection after intra-muscular injection, but not after oral delivery. We found that intra-muscular injection of this vaccine induced a strong local response as well as a virus-specific B and T cell memory response. Furthermore, we characterized the immune response to non-successful vaccines and we discuss possible ways for improvement. By developing new assays we significantly increased our knowledge and understanding of B and T cells in common carp and we characterized their roles during infection and after vaccination.