Nelma (lat. Stenodus leucichthys nelma (Pallas)) is traditionally considered a delicious "royal" fish, comparable in taste to sturgeon. In Russia, this fish naturally lives in the river basins of the Arctic Ocean and the Northwestern region, and abroad — in the river basin of North America. Nelma is attractive for rearing in aquaculture primarily for its excellent taste quality, as well as the presence of a large number of macro ‐ and micronutrients necessary for the human body. Thus, the level of polyunsaturated fatty acids in the nelma meat reaches 10.01±0.27, while the level of the saturated was only 3.87±0.22 mg/100 g. In terms of the ratio of these two fatty acid classes, the nelma is second only to sturgeon. The content of calcium is 1000, phosphorus ‐ 7800 mg/100 g, potassium ‐ 15 000 mg/kg, iron ‐ 25, manganese ‐ 1.2, copper ‐ 1, zinc ‐ 21, magnesium ‐ 0.76 mg/kg, vitamin A ‐ 1.06 mg/kg, E ‐ 26.67, B1 ‐ 10.67, B2 ‐ 6.4, B3 ‐ 11.96, B5 ‐ 81.5, B6 ‐ 7.11, B12 ‐ 106.7 µg/kg [2].
Recently, the nelma population in the reservoirs of the Ob‐Irtysh basin has decreased due to an increase in the intensity of nelma fishing and anthropogenic factors, so the catch of this species is prohibited in all southern and central regions of Siberia [4]. This situation requires constant work within the framework of artificial reproduction measures. Today, the most important scientific task fish farming enterprises face is the introduction of promising fish species, including nelma, into aquaculture, as well as the development of biotechnology for the full‐ cycle rearing of fish[1].
The problems of modern intensive aquaculture, characterized by a high density of growing objects, are fish stress, a decrease in immunity, which leads to an increase in morbidity, an increase in mortality and a decrease in the rate of development. Until recently, synthetic veterinary drugs, primarily antibiotics, were widely used in aquaculture to prevent these phenomena and reduce economic losses. Currently, the attitude towards the use of such drugs in animal husbandry and, in particular, in aquaculture is radically changing. It is proved that the usage of these drugs has an undesirable effect on the environment, contributes to the formation of resistant strains of microorganisms, the accumulation of toxic metabolites in the tissues of aquaculture species intended for human consumption. Therefore, in recent years, the mass use of such drugs is prohibited in many countries of the world. In this regard, alternative, the so‐called "eco‐friendly" methods are increasingly used in aquaculture effectively relieving the problems of aquaculture intensification, increasing its efficiency and productivity, but not having any negative impact on the environment. In this regard, the use of agents based on a number of food and medicinal plants — phytobiotics or phytogenics — is promising. According to Prasanta J. et al. [12], in various countries, about 250 plants from 75 families and 32 species are used for the production of such agents [12]. The biomass, agents (extracts and tinctures) of various parts of plants or phytochemical compounds isolated thereof are used as phytobiotics. Such agents exhibit stress‐regulating, antioxidant, immunomodulatory types of activity, are effective for combating pathogenic microbes, viruses, helminths and protozoa, contribute to the normalization of the digestive system function, increase the appetite and attractiveness of feed, improve feed conversion and, as a result, contribute to more effective weight gain. Phytobiotics are non‐toxic, eco‐friendly and economically more attractive than synthetic drugs, do not cause the development of tolerance due to the extreme diversity of the molecular composition of the molecules; they can be used both as part of the feed and when added directly to the aquatic environment [7]. According to the analytical agency ResearchAndMarkets.com, the market for phytogenic additives in agricultural practices, including aquaculture, is growing rapidly: in 2020, it was estimated at 753 million dollars, and by 2025, it is projected to increase to 1,098 million dollars with a compound annual growth rate (CAGR) of 7.8% [11].