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the aggregate of fishes of any body of water or basin of a zoogeographic region and the aggregate of fishes inhabiting the earth at any given period of its history. The ich-thyofauna of most basins is not uniform in origin; it is composed of species differing in their geographic origin and grouped in different faunal complexes. For example, the ichthyofauna of the Aral basin is composed of the highland-Asiatic faunal complex and of the Ponto-Caspian, the Turkestan, and other complexes. The diversity of the ichthyofauna is determined by the initial faunal complexes that formed a given ichthyofauna, by the history of the basin, and by present-day life conditions of the various species of fishes. As a rule, in the number of species the ichthyofauna of tropical waters is the more diverse, and most diverse is the ichthyofauna of the equatorial waters of the western Pacific Ocean. The poorest ichthyofauna is that of the arctic waters.