Trout are generally considered to be cool, freshwater fish species that belong phylogenetically to the rather young group of fin-rayed or Teleost fishes in the Family Salmonidae. Trout have significant economic, social and scientific importance. This book examines two 'trout', the rainbow trout Oncorhynchus mykiss and the brown trout Salmo trutta. This book came from the editor's interest to bring together some of the major areas that have made 'trout' such an important and enduring model species. The chapters have been carefully crafted by their authors to ensure that they cover as much of the topic as possible including references that support the information.