Endogenous nutrition - nutrition at the expense of internal resources of the organism. At all stages of development in the egg and immediately after hatching from the shells, nutrition of the embryo occurs at the expense of the stock of nutrients in the yolk sac, received from the maternal organism. Endogenous nutrition takes place in adult fish. For example, during wintering (carps, sturgeons), migrations (salmonids, whitefish, herring, eels, etc.) or in case of deterioration of habitat conditions (temperature increase, drying up or shallowing of water bodies), the vital activity of fish is maintained at the expense of energy resources accumulated during the previous period, primarily fat.