Here's why:
* Fish in general are cold-blooded. Very few fish species are warm-blooded (like tuna and some sharks), and fangtooth fish are not among them.
* They live in the deep ocean. The deep ocean is a cold environment, and fangtooth fish don't have the physiological adaptations necessary to maintain a constant internal temperature.
* Their metabolism is slower. Cold-blooded animals have slower metabolisms, which means they need less food to survive. This is an advantage in the deep ocean, where food can be scarce.
So, even though fangtooth fish have scary teeth, they are actually quite delicate when it comes to temperature control!