Although published under one name this book is the result of the work of many people. The knowledge has been acquired not only by scientists working on the topic as an academic problem but also by the fishermen who depend on their wisdom for the food they eat. During the course of travel to and on many of the worlds rivers I have benefitted from the friendship and cooperation of many who work directly with the fisheries described here and to them I owe an enormous debt. The scientists and fishery administrators of many countries have contributed considerably to this work through technical meetings of various types including the working parties of the FAO Regional Fishery Bodies dealing with inland waters. Much of the stimulus to collect and interpret this information comes from my colleagues in the FAO Department of Fisheries without whose help and encouragement it would be difficult to proceed. In this respect the many hours spent in the physical preparation of the paper by a number of secretaries should be particularly acknowledged.