A vaccine is a preventive tool used in a health management strategy for the control of infectious diseases in aquaculture.For more than 100 years,vaccines have proved to be an effective tool for preventing infectious disease outbreaks in humans,poultry and other food animals.In aquaculture,the development and use of vaccines is now making rapid progress to achieve its full potential as effective disease prevention tool.The objective of vaccination is to provide a strong immune response to an administered antigen able to provide acquired long-term protection against a pathogen.To achieve this objective either a killed or modified live vaccine needs to be developed and licensed for use in fresh or marine water aquaculture.The type of immunity needed,antibody and/or cell-mediated against,a particular pathogen is among the deciding factors in the development of a vaccine.Immunization with a killed bacterial vaccine produces an antibody-mediated protection,but not cell-mediated immunity.Cellular and/or antibody-mediated immunity can be provided only by immunization with a modified live vaccine.Further,antibody-mediated immunity provided by killed vaccines is relatively short lived in terms of protection(3-5 months).Longer protection(≥ 12 months)is provided by modified live vaccines.The duration of protection may be increased by the addition of an adjuvant to the killed vaccine.An adjuvant is a substance that increases specific immune responses against the co-inoculated antigen.Killed vaccines are usually administered by intraperitonal and/or intramuscular injection of individual fish.Injection is the least cost effective in terms of labor and time.Modified live vaccines may be administered by bath immersion to large numbers of fish(fry and/or eggs)which is a more cost effective method of mass vaccination in both labor and time.Killed vaccines are considered to be safer than modified live vaccines which may revert to virulence.Consequently,future trends include oral delivery of vaccines,immersion delivery of killed vaccines,development of additional modified live vaccines and multivalent vaccines and improved vaccine adjuvant and immunostimulant(s).This paper will present examples of new channel catfish and tilapia vaccines to examine some of advantages and disadvantages in the development and use of fish vaccines.