Is a Sailfish Ectothermic or endothermic?

Answer 1

Being the fastest fish, it is probably technically endothermic, like its close relative the swordfish, and several very fast, carnivorous fish and sharks. Many similar fish and sharks can at least regulate the temperature of their brain and eyes. Being warmer improves nervous system and muscular performance, and helps fish swim faster and hunt more effectively.

But this is obviously not the same as being "warm-blooded", which is why biologists don't like to use two overly-broad categories.

Answer 2

Sailfish are ectothermic animals, meaning they rely on external sources of heat to regulate their body temperature. They cannot maintain a constant internal body temperature like endothermic animals (birds and mammals) do.