Immune responses after injection vaccination of fish

During the last 20 years considerable progress has been made in describing and understanding the immune system of fish. Fish are the phylogenetically oldest vertebrate group with an immune system showing clear similarities to the defence systems of mammals and birds. Both innate immunity (non-specific responses) and acquired immunity (specific responses) are important for the defence against invading pathogens. Antigen injection will evoke humoral and cellular responses, which show the expected characteristics of specificity and memory. Variability in the results can be caused by external factors such as antigen dose, temperature and handling stress. Moreover, the genetic background of the fish may also play a role. The use of standardised inbred fish lines is recommended for the optimal development and evaluation of vaccines and vaccination procedures.