They act the same way as they do in water that's too cold. They will get lethargic They will stay near the top of the tank to breath. You will notice them panting. Try to keep them in the shade in the coolest part of the house. Put a good thermometer in the tank and keep an eye on the temp. In drastic heat a water change would be good but only reduce the temp by no more than 2 degrees in a 6 hour period. Water changes of colder water will send your guy into shock, and you will run the risk of Ick and fungus infections. Not to mention Death.