Domesticated animals of many species, including fish, have a set of physical and physiological characteristics that are not manifested in any of their wild ancestors, the so-called "domestication syndrome" first identified by Charles Darwin [22]. When animals are domesticated under conditions of artificial selection and isolation from the original (wild) form, their genetic properties change. There are literature data supporting the assumption that domesticated species differ from wild ones by increased activity of transpositions of mobile genetic elements [7]. People began domesticating fish much later than other animals. Carp (a descendant of the wild common carp), represented by various breeds and adapted for breeding in ponds is the most important fish that can be considered domesticated and, accordingly, changed under the influence of human economic activity. Other species of fish of the family cyprinids, sturgeons, salmonids, catfish, etc. have been domesticated as well. In our country breeds and crosses of fish of the following families have been created: cyprinids (Cyprinidae), salmonids (Salmonidae), sturgeons (Acipenseridae) [18].
Wels catfish (Silurus glanis, L.) (Fig. 1) is a valuable fish with high-protein and lowbone meat. Biological features successfully fit its cultivation at all stages of growth into the production technology of commercial fish in carp fish farms. An important feature of the catfish, in contrast to other predatory fish, is its proximity to carp regarding their demands for the main indicators of the chemical composition of the fish pond water and its transparency. If carp, the main object of pond fish farming, feels good in a fish farm, then we can say with a high degree of confidence that these conditions are also suitable for catfish. Catfish also tolerate temporary high water turbidity (during the descent and fishing of ponds, where catfish were reared together with carp).
This species has a wide food spectrum: fish, frogs, tadpoles, aquatic insects and crustaceans, dead fish. Consequently, catfish is often called a biological ameliorator. The ameliorative effect of growing catfish in polyculture results in the increased productivity of the main object of polyculture — carp. Carp fish-rearing ponds are characterized by an increase in the overgrowth of fishbreeding areas with aquatic vegetation to up to 25%, which favorably affects catfish growth and development rate since macrophyte thickets are a necessary condition for the survival, spawning, feeding, and recreation of wels catfish. Catfish are resistant to a number of common carp diseases. Breeding catfish in polyculture with carp and other types of pond fish makes it possible to obtain up to 1 centner/ha of a commercial two-year-old catfish weighing 0.9–1.2 kg [13]. Thus, the prerequisites for the domestication of the wels catfish are obvious. However, the absence of broodstock and seedlings in fish farms hinders its implementation in fish-breeding polyculture [14].