Today fish are no longer seen as simply prey to man's obsession with catching things, but have become important indicators to the health of any water body, as well as a fascinating area of our fauna. In this treatise on freshwater fish, the authors analyze the reasons for the paucity of British fish species as well as identifying reasons for a particular species' distribution. They discuss the biology and its effect on the ecology of each species, including methods of investigation, distribution, habitats, conservation, rare and endangered species and identification.