Is fish an animal?

Animals are found widespread in every corners of the globe, and yes, including the salty waters of the ocean and freshwater habitats of lakes, ponds and rivers.

We know that the whales, dolphins and porpoises are aquatic animals that belong to the mammalian class, and so are the sponges with all the perforations that cover up more than 90% of their bodies too. But what about fishes? Certainly not all that lives in the ocean (including the 91% of species that are yet to be classified) is an animal!

In this article, we discuss whether or not fishes are members of the animal kingdom.

Is fish an animal?

Yes, fish is an animal. It belongs to the basic group of animals referred to as ‘fish’ or ‘Pisces ’. The other five groups include: invertebrates, amphibians, reptiles, birds and of course mammals like you and me.

Fishes are regarded as animals because they fulfill the necessary criteria that qualify any organism to be classified as an animal. Below are some of the most popular criteria in details.

Why is fish considered an animal?

Fish is regarded as an animal because it posses all the traits that help distinguish animals from living organisms of other kingdoms.

All living organisms are divided into three domains and six kingdoms by the way, the domains include: Eukarya, Archaea and Bacteria, while the kingdoms include: Animals, Plantae, Protista, Fungi, Eubacteria (true bacteria) and Archaebacteria (ancient bacteria). The first four kingdoms belong to the Eukarya domain, the Eubacteria belongs to the Bacteria domain and the Archaebacteria belongs to the Archaea domain.

Some of the characteristics that helps distinguish animals from organism of other kingdoms include:

  1. All animals have multiple cells although the number of cells can vary greatly across different species; Roundworm C. elegans for example has 1031 cells no more no less, while humans, who are more complex creatures, have cells in the excess of trillions. Multiple cells helps distinguish animals from Archaebacteria and Eubacteria but not from plants, protists and fungi because they too have multiple cells.
  2. All animals have an eukaryotic cell structure, meaning that their cells have true nucleus and other specialized structures called organelles, and these cells are capable of grouping together to form a multicellular organism. Eukaryotic cell structure helps distinguish animals from Archaebacteria (ancient bacteria) and Eubacteria (true bacteria) but not from plants, protist and fungi because they too have an eukaryotic cell structure.
  3. Most but not all animals are capable of reproducing sexually. Sharks for example are able to reproduce asexually. Sexual reproduction helps distinguish animals from Archaebacteria but not from plants, protist, eubacteria and fungi because they too can reproduce sexually.
  4. Ability to move in at least one lifecycle stage of theirs is also one of the distinguishing features that every animal posses as opposed to plants and fungi.
  5. All animals cannot produce their own food but rather, must consume other organisms to in order derive sustenance. This is known as heterotrophy and it helps distinguish animals from most plants (which are able to manufacture their own food) but not from fungi and bacteria.
  6. Advanced nervous systems and specialized tissues too like nervous tissues, muscles tissues or connective tissues is perhaps the only distinguishing feature that sets animals apart from all other living organisms.

Several other traits aside from the ones mentioned above also exists too which distinguish animals from other living organisms. While each trait on its own isn’t sufficient to serve as a distinguishing characteristic, all of them, considered collectively, is what helps to construct the fine line between animals and other living organisms. 

Taxonomic classification of fishes

Fishes are abundant vertebrates found in the oceans, rivers and lakes. They belong to the vertebrate group of animals referred to as Fish or Pisces. They are classifies under the phylum chordate (moving back on the phylogenetic tree) under the kingdom Animalia and ultimately they belong to the Eukarya domain. Here’s what the classification looks like in a neat and arranged fashion.

Fish taxonomic classification

Domain (Eukarya)
Kingdom (Animalia)
Phylum (Chordate)
Class (Fish)
Sub-class (Main groups)
— Cartilaginous fish
— Bony Fish
— Jawless Fish

Whales and dolphins are mammals not fishes

Although fishes normally take habitat in aquatic environments, not all in the waters that looks like a fish is actually a fish, and this is especially true for whales and dolphins.

Whales and dolphins belong to the group (or class) of animals known as mammals which can be distinguished from fishes (and other animals) by many unique traits, some of which include:

  1. They have mammary glands which are nothing but modified sweat glands that produce milk for suckling offspring. Only mammals have mammary glands and sweat glands.
  2. They breastfeed and tender for young ones unlike fishes that abandon their babies upon birth.
  3. Most of them give birth to young ones alive but altricial. This means that the young require sufficient care from their parents in order to be able to survive through to independence.
  4. They breath using lungs unlike most fishes that breath using gills.
  5. They are endothermic (warm blooded) unlike most fishes that are ectothermic (cold blooded).
  6. The have three middle ear bones.
  7. They have a single bone in their lower jaw that articulates with the skull.
  8. Dolphins have molars they use for chewing (which is a trait peculiar only to the mammalian class).

You can learn more on “why whales are mammals instead of fishes“ by visiting the link below.

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Cite this Article (APA Format)

Bunu. M. (2020, May 21). Is fish an animal?. Retrieved from

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