Question: are fish ectothermic or endothermic?
Answer: Endotherms and ectotherms Iguanas and rattlesnakes, like most other reptiles—along with most fishes, amphibians, and invertebrates—are ectotherms. Endotherms generate most of the heat they need internally. When it's cold out, they increase metabolic heat production to keep their body temperature constant.