Which category do fish, the majority of invertebrates, and amphibians belong to based on their body temperature regulation?

Explanation

Fish, most invertebrates, and amphibians are classified as ectotherms, meaning their body temperature depends on the external environment rather than internal heat production. Endotherms (warm-blooded animals) regulate their body temperature internally, while heterotherms have variable temperature regulation, and homeotherms maintain a constant body temperature.