This book provides a synthesis of taxonomic and ecological information on New Zealands freshwater fish fauna. New Zealand has been isolated in the southwestern Pacific Ocean since it separated from Gondwana during the Cretaceous period, some 80 million years ago. This prolonged geological isolation, combined with the islands very vigorous geological history, impacted by oceanic submergence, tectonic activity, mountain building extreme volcanism, and great climatic variability, create a dynamic scenario within which the New Zealand biota, including its freshwater fishes, have evolved over millions of years. These impacts have contributed to a highly dynamic biological history with undoubted though little understood extinction and vigorous colonisation of the islands fresh water. One of the key elements for understanding the origins and derivations of this fish fauna is that in all groups some or all of the species are diadromous, customarily spending a significant phase of their lives at sea. This has no doubt contributed in an important way the faunas origins As well, there has been frequent loss of diadromous behaviours leading, to species that have abandoned their sea-migratory behaviours and which now complete their entire lives in fresh water. The distribution patterns reflect these changing habits, with diadromous species being broadly distributed but tending to be lowland in range, whereas the derived, non-diadromous species have narrower ranges, but are often found further inland and at high elevations. This book provides an ecological and historical synthesis of these divergent patterns across New Zealands geography and history.