 Fish are cold @-@ blooded and in general , their body temperature is the same as that of their surroundings . They gain and lose heat through their skin and during respiration and are able to regulate their circulation in response to changes in water temperature by increasing or reducing the blood flow to the gills . Metabolic heat generated in the muscles or gut is quickly dissipated through the gills , with blood being diverted away from the gills during exposure to cold . Because of their relative inability to control their blood temperature , most teleosts can only survive in a small range of water temperatures . 
