The diversity of environmental conditions (water depth, lowage and weediness of waters) found in water reservoirs of the Reserve accounts for the diversity of fish species (a total of 56 species belonging to 12 families). The most abundant are Cyprinidae (24 taxons) and Agonidae (11 taxons). The region is a global scale center known for the diversity and wealth of its fish fauna, with special emphasis on the diversity and richness of sturgeon species (Acipenseridae). Huso huso, Acipenser gueldenstaedti, A.stellatus are common here, A.ruthenus can also be found in the Reserve. Among the fish fauna of the Reserve the most common species are freshwater species, mainly Cyprinidae and Percidae: carp, bream, Caspian roach, tench, rudd, silver bream, asp, lookup, and also pike, cat fish, river perch, pike perch, crucian carp and several species of Cottidae, while nase, сопа, sabre fish and Volga zander are found rarer. Diadromous and semi-anadromous fish, which migrate to the Reserve’s area during the spawing season, represent quite a considerable portion of the Reserve’s fish fauna, another considerable part of which are marine fish. Anadromous fish species – Acipenserodae and Clupeidae – can be found in the Reserve’s waters only when they migrate from the sea to their spawing grounds in the Volga River and back. There are ongoing changes in the water reservoirs of the Reserve driven by welldefined delta-formation processes. These changes include the weediness of some water bodies and deepening of others, that results in close neighborhood of sites with different environmental conditions (plant composition, hydrologic and thermal regimes). This brings species of different living conditions to coexistance. Those fish species that prefer to live in open water, e.g. silver bream, asp, ablet, perch and pike perch, occupy large and middle-size waterways and eriks of the subaerial Delta, which also serve as migration paths for diadromous and semi-anadromous fish. Inhabitants of vegetated waters, such as rudd, tench, crucian carp, perch, ruff and spined loach, dominate in the reservours with slowly running water (erickas, il’mens and kultuks) Marine fish, mainly sculpins, are also found in the subaerial Volga Delta. The avandelta is a zone where representatives of marin fauna (sculpin, pipefish, stickleback, assous) mix with typical freshwater species (pike, tench, rudd, silver bream, crucian carp, cat fish). The significance of freshwater fish reduces as one goes downstream. Many of the Reserve’s reservoirs and
waterways are migration paths or spawing grounds of fish. The main spawing grounds are inundated meadows (also called poloys) of the subaerial Delta. The water get warm very early here giving rise to the rapid development of hydrobionts. Vegetation grown up before the beginning of the spawing season serves perfectly as a substrate for fish roe. In July-August fry leave the spowing grounds. Those young fish, which are late to enter the river, perish in detached reservoires. Those, which timely left the grounds, gather in the avandelta. By the middle of summer the avandelta’s water is warmed up and covered with water vegetation, so it provides young fish with a shelter and food. Besides being a feeding ground for young fish, the avandelta serves as a secondary spawing ground for intermittently spawing species. In autumn some fish species migrate to their wintering basins. Cat fish and carp gather and spend winter dormant in large swims. Not only fry but also larger fish have great significance for the nutrition of birds, animals, amphibias and reptiles inhabiting the Reserve, in every season excepting the time when water is covered with ice.