In order to substitute the differential equation for one-dimensional refrigeration of fish with a system of equations in terms of finite differences, suitable to numerical calculations, special attention was paid to the change in temperature during the interval of time, in which the freezing commences layer by layer, from the outermost surface of fish exposed to the cooling medium to the interior parts. Suppose a plate-like flesh of fish is divided into layers of finite small thicknesses. If the temperature distribution is given at the instant, when the i-th layer begins to freeze, the equations obtained give the drop in temperature at each layer, as well as the time taken, till the next i+1-th layer begins to freeze.
