Most of us want to know the answer to the question that “are fish mammals or classified in some other category?” The simple answer is; No! Fish are not mammals. Fish and mammals both lie in the phylum Chordata – that means the animals with notochord – but fish is another class different than mammals.
1. What are fish classified as?
Vertebrates!
According to the theory of evolution, all the animals have been evolved from a single ancestor. Animals are mainly categorized as vertebrates and invertebrates.
These two groups differ from each other based on the presence or absence of the backbone.
Vertebrates:
Vertebrates are those animals who have a backbone in their body that helps them maintain their posture, such as birds, mammals, fish, etc.
Invertebrates:
Invertebrates are animals that lack a backbone such as mollusks, insects, jellyfish, and annelids, etc. Animals of this class either have a soft body – such as worms – or they have a hard exoskeleton – such as crabs.
Fish are classified as vertebrates as they have a well-formed backbone. They are water animals and about 34,000 species of them are present in the water bodies.
1.1. Classification of fish
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Animals have been classified according to their similar features and the differences from the other groups.
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Living organisms with similar features or characteristics are placed in the same division.
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A brief classification of fish is given below to clearly understand that either the fish are mammals or not.
| Taxonomic division | Vertebrates |
|---|---|
| Kingdom | Animalia |
| Phylum/ Division | Chordata |
Chordates present in the phylum Chordata are the animals that possess a notochord, a nerve cord, a pharyngeal slit, and a tail (post-■■■■) at a certain level of their life cycle.
1. Notochord is the cartilaginous skeleton-type rod that supports the body.
2. Nerve cord is the major cord consisting of the nerve fibers that run across the length of an animal’s body.
3. Pharyngeal slit are the openings that are present along the pharynx and allow the movement of water in and out the mouth.
4. Post-■■■■ tail is the elongation of the body that extends beyond the ■■■■ and acts as a source of locomotion to the aquatic animals.
1.2. General features of fish
Fish is a large group of animals living in water bodies. They are taken as a distinct life-line instead of a separate taxonomic division.
Just like the question that what color are elephants, there is mostly a confusing question that is fish mammals or classified in some other category?
Actually, the fish are not mammals - although the whales and dolphins that are normally considered as fish are the warm-blooded mammals.
There are some distinct anatomical features of the fish that make them different from the other animals.
1. They have fins
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A main feature of the fish is that they have fins.
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Just like the fore and hind limbs of human beings, these fins help the fish maintain their balance, in protection and steering.
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There are the following types of the present along the centerline of the fish:
| Single fins | Function | Paired fins | Function |
|---|---|---|---|
| Dorsal fins | Balance, and protection | Pectoral fins | Help in maintaining balance |
| ■■■■ fins | Help in steering and balance | Ventral fins | Same as ■■■■ fins |
| Tail fins | Helps moving forward |
2. They have gills
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Gills are the special feature that makes them different than the other vertebrates or chordates.
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They are present on both sides of fish and help them getting oxygen from the water.
3. Covered with scales
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Body of the fish is covered with scales.
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Scales perform the same function for fish as the skin does for humans.
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They protect their body from injury.
4. Distinct body and mouth shape
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Body shape of the fish is designed in such a streamlined way that it helps them swimming in the water just like the Aeroplan can fly as it has a specific shape.
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Moreover, body shape also tells a lot about the type of aquatic habitat in which a fish lives.
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Different species of fish have different types of mouth and it can be with or without teeth.
Summary
Fish are not mammals because they have some distinct features that are not present in mammals. They have single and paired fins, have gills, possess scaly skin, and a special streamlined body with various types of mouth for each species.
2. Are fish reptiles or amphibians?
Just like the question, are fish mammals or not? There is another most asked question that is fish reptiles or amphibians?
Although fish, amphibians, and reptiles all are present in the class vertebrae, yet fish are not classified as reptiles or amphibians. Fish have a separate division other than the reptiles, mammals, and amphibians.
To better understand the reason for classifying the fish other than as being reptile or amphibian, it would be fine to discuss that what are reptiles and amphibians.
2.1. Reptiles
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Reptiles are tetrapod animals – that move with four limbs – and have scaly skin.
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They are cold-blooded animals and spend their lives on the land.
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This is the reason in extreme winter and summer, reptiles mostly undergo hibernation.
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They are vertebrates and present in the class Reptilia. Most of them lay eggs.
Snake, turtle, lizard, and crocodiles.
2.2. Amphibians:
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Amphi means two. Hence amphibians are the animals that spend half of their life on land and half in water.
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They are vertebrates and require water or a moist environment for their survival.
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They have thin skin and can breathe through the skin.
Frogs, salamanders, toads, etc.
So, after considering all the properties of reptiles and amphibians, it’s clear that fish are neither reptiles nor amphibians.
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3. Are sharks fish or mammals?
Same as the question, are fish mammals or not, another confusion arises in the mind of people is the question are sharks’ fish or mammals.
Fish are aquatic animals that lack segmented limbs. Whales and dolphins that are normally considered as fish are warm-blooded mammals.
Fish and mammals both lie in the phylum Chordata – that means the animals with spinal cord – but fish is another class different than mammals.
Before going into details about the sharks being mammal or not, the first thing to be clear is that what are mammals and what are their salient features?
3.1. What are mammals?
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Mammals are the animals present in the vertebrate group that gives birth to their young ones.
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They constitute the class “Mammalia” and that term is originated from the “mammary glands”.
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As the mammals are those animals that feed their younger ones and mammary glands produce the milk. Hence the name mammals are given to this taxonomic division.
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A second character that mammals have is the presence of the neocortex – a six-layered part of the brain – that is involved in the higher brain functions.
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the Third character of mammals is that they have three bones in the middle ear that are named – malleus, incus, stapes.
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the Fourth characteristic is that mammals have fur or hair on their external body surface.
3.2. How sharks are fish?
Sharks are a type of fish. They have skeleton-like mammals but they are cold-blooded as compared to the mammals that are warm-blooded animals.
Cold-blooded animals are those animals that are not capable of adjusting their body temperature according to the surroundings.
Warm-blooded animals can change their body temperature according to the environment and are able to maintain a constant internal body temperature.
1. Sharks don’t have mammary glands
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Mammals are regarded as mammals as they have mammary glands.
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As sharks don’t have mammary glands and don’t feed their younger ones, then how can they be regarded as mammals?
2. They are cold-blooded
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According to the distinctive features of mammals, they are warm-blooded animals and can regulate their body temperature.
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As sharks are cold-blooded and aren’t able to maintain their body temperature according to the surroundings, they can not be classified as mammals.
3. Sharks lack fur and body hair
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Another feature of mammals is that they have hair or fur on their body skin.
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Sharks don’t have hair or fur on their body surface and it makes them different from mammals.
4. Sharks have gills
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Gills are the specific character of fish and are used to help them in breathing.
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Water is taken through the mouth and expelled via gills and during this process, fish fulfill their need for oxygen.
5. Sharks lack middle ear bones and neocortex
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As previously explained in the characteristics of mammals, neocortex and middle ear bones are the salient features of mammals.
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Sharks lack these structures and hence can’t be considered as mammals.
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4. Are dolphins fish or mammals?
Dolphins are mammals, although they spend an aquatic life yet they are classified as mammals.
Dolphins meet the criteria to be classified as mammals as they are also warm-blooded just like mammals.
This question arises along with the confusing question that either the fish are mammals or classified in some other category?
Answer is simple No; Fish are not mammals. Although whales and dolphins that are normally considered as fish are actually warm-blooded mammals.
Fish and mammals both are present in the same phylum Chordata – that means the animals with spinal cord – but fish is another class different than mammals.
1. Dolphins are warm-blooded
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Main feature of the mammals is that they are warm-blooded animals – that means the mammals can maintain their body temperature according to the surroundings.
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Dolphins are warm-blooded animals and hence classifies as mammals.
2. Dolphins breathe through lungs
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A point of amazement for those who didn’t know this is that the dolphins although spend their entire life in the ocean, yet they don’t have gills.
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They breathe through the lungs and for breathing they have to make frequent visits to the surface of the water where they inhale the air.
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Nose is present as blowhole on the top of dolphin that makes the breathing easy for them.
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This absence of gills makes them different from the fish and similar to the mammals.
3. Dolphins give birth to younger ones
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Yet another important feature that makes them similar to the mammals and clearly distinct to the fish is that they don’t lay eggs.
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Dolphins give birth to their younger ones and also feed them, unlike the fish.
4. They have hair on their body
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Moreover, hairs are also present on the body of dolphins – around the nose/ blowhole.
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Presence of hair on the body is the characteristic feature of mammals.
In short
Dolphins are mammals as they have all the features of mammals. They give birth to young ones, feed them with milk, breathe through lungs, and have a small quantity of hair near their nose or blowhole.
Frequently asked questions
Are fish mammals or not is a question that arises several other questions in the mind of people. Some of them have been tried to be answered briefly:
1. Why are fish not mammals?
Fish are not mammals because they lack the following characters that are the characteristic features of mammals:
- Fish don’t give birth to their younger ones.
- They don’t have mammary glands and don’t feed their offsprings.
- They have scales and not the hair on the body.
- They don’t have middle ear bones and neocortex.
Whales, dolphins, seals, sea lions and otters are all mammals although they spend their whole life in the aquatic environment.
2. What type of mammal is a whale?
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Whales although are aquatic, animals, yet are classified as mammals.
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They are warm-blooded, placental animals and breath through lungs just like mammals.
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Whales also give birth to their young ones but because of the lack of lips, the young ones cant suck milk.
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Milk is injected into the mouth of a baby whale until they start eating solid food.
3. What type of animals are fish?
Fish are classified in a separate group according to the classification of animals. This classification consists of the following taxonomic groups:
- Mammals
- Birds
- Fish
- Reptiles
- Amphibians
So, fish are classified as vertebrates and included in the class of chordates – animals that have a notochord. Fish are neither reptiles nor amphibians and have almost 34,000 species.
Conclusion
A mostly asked question “are fish mammals”? can be answered in a single word “No!” fish are not mammals.
Although some aquatic mammals – such as dolphins, whales, and seals – are wrongly considered as fish, yet fish have their own class other than mammals, amphibians, and reptiles.
Whales and dolphins share are the distinctive characters of mammals and hence classified as mammals. While sharks are belonging to the typical class of fish as they have no similar feature to mammals.
Fish have the following characteristics that make them different from mammals:
- Fish have fins.
- They have gills.
- They lay eggs.
- They don’t feed their offsprings.
- They don’t have middle ear bone.
- They have a streamlined body that helps them to swim.
- They don’t have body hair instead they have scales.
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