Are Fish Considered Mammals

Are Fish Considered Mammals?

The oceans of the world are magnificent places, full of all kinds of life and wonders. Over thirty thousand different species of animals make up the trillions of living organisms that call the oceans of the world their home. A commonly asked question is, are these fish mammals?

Fish are not mammals as most do not have warm-blooded, nor do they feed their young with milk. Most fish don’t breathe air, nor do they have lungs. Thus they are considered aquatic vertebrate animals. There are a few ocean animals that are considered marine mammals, such as various species of whales, dolphins, and porpoises. 

This article will discuss whether or not fish are mammals and the reasoning behind it. So keep reading! We have everything you need to know about whether or not fish are mammals. 

What Are Fishes Considered?

Trillions of fish live in our oceans, and thousands of species make up this total number. When it comes down to what a fish is, however, some may assume they are primarily mammals, others that there are a vast amount of amphibians, whereas some may just call them fish. But what is the correct answer?

Fish are considered aquatic vertebrate animals, meaning that they have internal backbones. They have gills that enable them to breathe underwater. However, they do not have limbs, fingers, or toes on any part of their body. 

Defining a fish can sometimes be confusing as the word itself includes many sub-categories and usually depends on which context you use it in. When you are talking about all the animals that live in the ocean, if you use the word fish to define them, this can be considered the wrong definition. 

Marine mammals are not technically fish, even though they live in the water. They have all the characteristics of a mammal, such as fur (even if it’s minute), and they feed their offspring via milk which they produce. 

When we talk about fish as opposed to animals that can live in the ocean, we can divide them into three rather large groups;

Chondrichthyes: These are fish that have skeletons formed from cartilage and not bone. This group consists of sharks and rays. This means sharks are not mammals, as all mammals have skeletons made of bone. 

Agnatha: These fish do not have jaws, fins, or stomachs in some cases. This includes fish such as lampreys and hagfish. 

Osteichthyes: This category of fish is the largest and contains just about every other fish, which isn’t included in the former two. These are defined as fish that have skeletons made of bone. 

What Type Of Fish Is A Mammal

Certain animals that live in the ocean are technically considered mammals and not fish because of certain traits that influence their lives and offspring. There are a few ocean animals that we refer to as marine mammals, as they are technically mammals that live in the ocean. 

Dolphins and whales are two examples of marine mammals, as they exhibit the typical characteristics of mammals. This includes; having to breathe air, being warm-blooded, their bodies grow small amounts of fur, they give birth to live young, and their bodies produce milk which is used to feed their babies. 

Although whales, dolphins, and porpoises look a lot like fish and can live in the water for an extremely long period of time, they are usually not considered fish in the same way as tuna or a shark. The better definition is a marine mammal, as they still need to visit the water’s surface to breathe frequently. 

Are Fish Considered Amphibians?

A category of animals lies in the middle of being both a fish and, to some degree, a land animal, and this species is known as an amphibian. Unlike fish, some amphibians have the ability to breathe oxygen in the air, yet they have to breed in the water.

Like most fish, amphibians are vertebrates with smooth and slimy skin. They can breathe in the water through this skin, but in some cases, they can breathe through their lungs. They are cold-blooded animals and have a complex life cycle. 

Amphibians will lay eggs, usually referred to as spawn, in still and fresh water, hidden among plants. They produce babies known as tadpoles which are born with gills but will soon develop lungs and legs. Once they reach adulthood, amphibians will spend most of their lives on land, usually only returning to the water to breed in the spring.

So, in reality, fish are not amphibians as they do not spend any of their life on land. In comparison, amphibians such as frogs, toads, newts, salamanders, and caecilians can live both in the water and on land for an extended period. 

Are Dolphins Mammals Or Fish?

Dolphins are some of the most intelligent marine mammals scientists have ever studied. Known for their tribal groupings, playtime, and hunting skills, they have brains that could put any human to shame. 

When it comes to classifying these ocean animals, while they may be mistaken for fish due to living in the ocean, they are referred to as marine mammals due to many of their characteristics.

Dolphins, unlike fish, are warm-blooded like every other mammal, and they do not breathe using gills like fish. Instead, they must return to the surface to breathe through their lungs periodically. The blowhole located on the top of a dolphin’s head acts as a kind of nose when the dolphin reaches the surface of the water. 

One of the primary reasons why we can say with confidence that dolphins are mammals is because, like every other mammal on the planet, they give birth to live young and then proceed to feed them via milk produced in their bodies. 

On top of this, like most land mammals, dolphins have a portion of hair found around the area of their blowhole on the top of their head. Because of all these points, scientists now recognize dolphins as mammals or marine mammals instead of large fish. 


So, within this article, we have shown that while fish are not mammals, certain animals live within the ocean that can be considered marine mammals and spend most of their life in the water, such as dolphins and whales.