The techniques of molecular biology offer a powerful means of investigating and controlling the genetic basis of mechanisms operating in living organisms. The development of these techniques in aquatic animals has now reached the stage where important questions relating to growth, development and adaptation to the environment can be addressed at the level of gene expression, and the introduction and expression of novel genes achieved. This volume presents some of the most exciting advances in this rapidly expanding area, with contributions on the evolution of adaptation to low temperature, adaptation to short-term fluctuations in temperature and salinity, gene expression during growth and development, myosin polymorphism and the generation of transgenic fish. As such, it will be of interest to all those working in the fields of marine and freshwater biology and also to those working in aquaculture.