Is a fish an Endotherm?
Though rare, some fish are able to internally regulate temperature. Unlike ectotherms, which rely upon environmental temperatures, endotherms are able to metabolically control their body temperature.
Are most fish ectotherms?
Although most fishes are strictly ectothermic, there are (of course) also fish that attain a regional endothermy in important organs and tissues, such as muscles, eyes, visceral organs, and the brain (69).
Are mammals and fish ectotherms?
In vertebrates, endothermy is typically associated with birds and mammals while fishes, amphibians, and reptiles are generally typified as ectotherms.