The aim of this work was to determine the effect of an abrupt growth in temperature (from 24 to 35°C) on the FFA level in carp plasma, for the fish kept in water without and with Relanimal at concentration of 0.5 ml/l. It was noted, for the fish kept in pure water, the FFA level in fish plasma to decrease, respectively, by 20 and 70% after 15 and 30 min. exposure to increased temperature. With the Relanimal added the FFA in carp plasma, decreased by 5.4 and 10.8% respectively, after 15 and 30 min. exposure.