Mechanisms of metabolism regulation in carps during wintering in natural conditions (review)

A pressing issue of modern industrial aquaculture is the organization of carp overwintering in natural waters. At winter a lot of stressors affecting the fish negatively influence it physiological parameters, increase morbidity and mortality and reduce productivity. The main extreme factors are prolonged exposure to low water temperatures (cold stress) and oxygen deficiency (hypoxia). However, carps are able to successfully withstand these stressors, and a high tolerance to ones is determined by evolutionarily developed adaptive mechanisms. Resistance to hypothermia in carps is associated with transcriptional responses that regulate the expression of a number of genes, while tolerance to hypoxia is associated with the development of specialized metabolic systems. These mechanisms adapt carp to overwintering by inducing a hypometabolic state, which is associated, among other things, with reduced motor activity and cessation of food intake. During wintering, fish rely on internal energy resources to maintain their vital functions. Depletion of these resources leads to decreased resistance, the development of pathological processes, and a slower growth rate. A significant information criterion for assessing the energy reserves of carp is the Fulton body condition factor K. Determining this factor in fish in the fall allows one to predict the survival rate of fish during the upcoming wintering period, while comparing K values between fall and spring allows one to predict the fish’s development prospects. Increasing the K factor during summer carp maintenance using enriched feeds helps reduce fish mortality during wintering.