AQUAFIRST seeks to identify genes associated with stress and disease resistance in fish and molluscs to provide a physiological and genetic basis for marker-assisted selective breeding. It builds on earlier EU funded projects: BRIDGEMAP, BASSMAP and STRESSGENES. To counter poor growth performance, impaired reproduction and increased susceptibility to disease, growers have increasingly used antibiotics and drugs. The development of selective breeding programmes using genetic markers offers a means to reduce, if not eliminate, the use of antibiotics.