Organic compounds. They are active groups (cofactors) of enzymes, which are necessary in small quantities for the normal development and growth of fish. The lack of vitamins inevitably leads to a malfunction of metabolic processes, which negatively affects the development, growth, productivity and reproduction of fish. The absence of vitamins in fish feed results in vitamin deficiency. This is usually caused by an extremely monotonous diet. The limited content of vitamins in feed causes hidden forms of deficiency - hypovitaminosis - which can be very damaging to fish farming, especially in industrial farms and where fish are densely planted in ponds. The result is an increase in fish mortality, a decrease in their growth rate, a deterioration in the efficiency of the use of compound feed, and an increase in production costs.