The paper deals with the influence of different feed quality on the chemical composition and features of nutrient accumulation in the somatic muscles and hepatopancreas of two-yearold carp species. Fish were fed using pendulum auto-feeders on demand with K-111 compound feeds (23% protein and 3.5% fat) and Karp 38/12 (38% protein and 12% fat). In variant I, K-111 compound feed was used (in both car feeders), in variant II – Karp-38/12 (in both car feeders), in variant III–K-111 and Karp-38/12 (in different car feeders). The bionic method allows identifying the preference of fish for a particular type of feed. Regardless of the diets used, the water content in organs and tissues decreases during the growing of two-year-old carp species, which is primarily due to the accumulation of fat. To a lesser extent, this is due to the number of dry fat-free substance.

The results of research on the effect of feed with different feeding values and organoleptic properties on the productivity of two-year-old carp are presented. Within the same pond, the joint use of demand feeders (feeds with different tastes) makes it possible for fish to choose one of them in response to well-developed chemoreception. Diets of different calories affect the quality of the resulting fish production at different feed consumption. The combination of two feed types within one pond provides fish food savings per gain, despite the higher total consumption. Two-year-old fish give preference to more high-energy fish food. At the same time, fish consume 1/3–1/4 of low-energy food, regardless of the feeding time. The mass of fish consuming only low-energy fish food is 1.7 and 2.6 times less than that of fish consuming only high-energy fish food and fish simultaneously consuming these two foods, respectively. Combined feeding contributes to an increase in the relative muscle mass, primarily in comparison with fish fed only a high-energy diet. Fish-farming biological characteristics indicate higher fish yielding qualities in the case of simultaneous use of two types of feed (K-111 and Karp-38/12). Taste priorities must be considered in aquaculture fish farming.

The article provides data on the use of auto-feeders for the free choice of compound feed of different composition by two-year-old carp. Self-feeding is one of the ways that make it possible for fish to receive the necessary nutrition, depending on their biological rhythms, regardless of the desire of a person. This method takes into account the concept of “appetite”, which has a significant impact on the rate of feed intake, thus providing the basis for the wellbeing of aquatic organisms. At the same time, the behavior of fish changes, which makes it possible to use food resources more advantageously for gaining body weight, which has been repeatedly shown. The production quality of fish depends not only on the method of feeding, but also on the composition of the feed, which meets the needs for nutrients and promotes their intensive growth. Low-calorie food K-111 does not allow two-year-old carp to show their potential, as evidenced by a smaller mass of fish than when using high-calorie Carp 38/12. Two-year-old carp fed a feed complex with different energy content do not grow the same way. From 18.06 to 11.10, the mass of the studied fish increased in variants I, II and III by 4.6; 7.9 and 9.8 times, and the length - by 66.1; 75.5 and 96.8%, respectively. The number of white muscles for 5 months of carp growing when using K-111 compound feeds increases by 11.3%; Carp 38/12 - does not change and K-111 together with 38/12 - by 17.6% (P<0.05). By loading auto feeders with only one type of feed, a person deprives the fish of the right to choose, and it must only eat it "without appetite." This, accordingly, affects metabolic processes, and, ultimately, growth in general. This is evidenced by our experimental results. When caught, the average weight of carp with combined feeding was 1220 g, which is 2.1 and 1.2 times higher than in fish from options I and II, respectively. Free choice of food allows you to grow fish with a high yield of muscle mass, due to a higher growth rate. When giving a choice, carp prefers high-calorie food (approximately ¾ of the diet), but at the same time does not neglect low-calorie food in a certain proportion (1/4 of the diet). The use of different quality feeds in one pond allows, in our opinion, to comply to a large extent with the Welfare conditions when raising fish. Thus, the use of automatic feeders with different rations in one pond enables the fish to fulfill their needs for a particular food. Such studies make it possible to identify favorable feeding conditions for the cultivation of various types of fish.

The paper provides information about the growth and development of somatic structures of two-year-old carp during the fattening period. In variant I, K-III compound feed was used (low-carb-monodiet), in variant II – Carp-38/12 (high-carb-monodiet), in variant III – KIII and Carp-38/12 (in different auto-feeders). The highest proportion of axial somatic structures was observed in fish of variant III (fish feeding on a selective basis) (P < 0.05). White muscles are also better developed in fish that eat complex feed (variant III). Compound feed Carp 38/12 does not increase the mass of white muscles (P < 0.05). The proportion of red muscles in fish that eat mixed feed with a low fat content (3.5%) is 45.5% lower than in variants II and III. The use of feed with different energy values and their combination in one pond affects the growth and development of the structure that determines the growth of fish species – the axial skeletal muscles. At the same time, the two-year-old fish species that received the most energy-intensive diet were the most well-fed. Two-year-old carp that received feed with different energy content and complex composition grow differently. This is primarily due to the growth of muscles, which is evidenced by allometric coefficients. The highest values of this parameter featuring positive allometry, were observed in two-year-old carp that received two compound feeds from different feeders (white muscles b = 1.106; red muscles b = 1.499; all muscles b = 1.125). The bionic method of feeding fish in combination with feeds of different energy values provides for strengthened growth of one of the most important body structures – the somatic muscle system. It is not only a biological component of the body that ensures the welfare of animals, but also a high-quality food source.