A dolphin is classified as a marine mammal , not a fish.

Basic biological classification

Dolphins belong to the following main taxonomic groups:

  • Kingdom : Animalia (animals)
  • Phylum : Chordata (animals with a spinal cord)
  • Class : Mammalia (mammals)
  • Order : Cetacea (whales, dolphins, and porpoises)
  • Suborder : Odontoceti (toothed whales, which include dolphins and porpoises)

Dolphin vs fish: why it matters

Even though dolphins live in water and look superficially fish‑like, they are warm‑blooded, breathe air with lungs, give live birth, and nurse their young with milk—all hallmarks of mammals. This means dolphins are more closely related to cows, whales, and even humans than they are to any true fish.

Types and families

Within cetaceans, “dolphin” can refer to several species across different families, including:

  • Delphinidae – oceanic dolphins (e.g., bottlenose dolphin, common dolphin)
  • Platanistidae, Iniidae, Pontoporiidae, Lipotidae – river and related dolphins

So the short answer to “what is a dolphin classified as?” is: a mammal in the order Cetacea, specifically a toothed whale in the suborder Odontoceti.

Info note: Information gathered from public forums or data available on the internet and portrayed here.