Question

why fishes are cold blooded

Answer 1

old-blooded animals, like reptiles, amphibians, and fish, become hotter and colder, depending on the the temperature outside. For example, when the sun sets at night, their bodies are cooler because it is less warm outside. When the sun is out, however, their bodies soak up the heat and become warmer

Answer 2

They are Poikilotherms(Cold blooded) because they are unable to maintain their body temperature according to the environment.