Global aquaculture is projected to grow from 10 million to 20 million metric tons by the year 2000. To meet this projection, the aquaculture industry must bring some of its infectious disease problems under control without relying on antibiotics and chemotherapeutics. Thus, vaccines for fish and shellfish are being sought by the industry. The very first commercial fish vaccine was a killed vibriosis bacterin which was very effective and relatively easy to produce. Vaccines for other bacterial, viral, and parasitic fish pathogens are proving more difficult to develop and researchers have begun to use molecular and biotechnological approaches to develop such vaccines. This review describes the vaccines that are now available as well as the vaccines that are being developed and includes a discussion of live, attenuated vaccines, immunoadjuvants, and subunit vaccines for fish.