From the Greek ichthys - fish and fauna.

Ichthyofauna - a set of fish species of a certain water body, river, reservoir or territory (region).

The aggregate of fishes of a water body, basin of a zoogeographic area, etc., as well as the aggregate of fishes that inhabited in a particular period of the Earth's history. The ichthyofauna of most basins is heterogeneous in origin; it is composed of species of different geographical origin and grouped into separate faunal complexes. For example, the ichthyofauna of the Aral Sea basin consists of the highland-Asian faunal complex, the Ponto-Caspian, Turkestan and others. The richness of the ichthyofauna is determined both by the original faunal complexes from which this ichthyofauna was formed and by the history of the basin, as well as by the current living conditions of various fish species. As a rule, the ichthyofauna of tropical waters is the richest in number of species; the richest is the ichthyofauna of equatorial waters of the western Pacific Ocean. Ichthyofauna of high Arctic waters is the poorest.