Dramatic changes have occurred in the functioning of larger rivers because of social values and policies, land use, inchannel causes, and alien species. These changes have resulted in the reduction in range and abundance of many native fish species. This book describes the historical changes observed in the fish assemblages of 27 large rivers in North, Central, and South America. A synthesizing chapter highlights common and distinct patterns among the rivers and their stressors. The book focuses on entire fish assemblages, including the many species that do not enter fisheries. It will be of interest to both fishery biologists and aquatic ecologists who are concerned with the status and trends in biodiversity and biointegrity. Contains historical information as well as new research and monitoring results, including research on metapopulations, genetics, and life history strategies.