This volume, the proceedings of the Fourth International Symposium on Genetics in Aquaculture, builds on the foundations laid down at the first symposium, held in Galway, Ireland in 1982 (Aquaculture, Volume 33), as well as those laid down at the second, held in Davis, California, USA in 1985 (Genetics in Aquaculture II), and the third, held in Trondheim, Norway in 1988 (Genetics in Aquaculture III). It addresses specific problems and developments in this field, demonstrating the tremendous breadth of research activity as well as the complexity of issues in aquaculture genetics. This book will be of great value to aquaculturists, fisheries scientists and marine biologists.(The above-mentioned proceedings of the first three conferences are still available).