Have you ever wondered if fish are considered reptiles or amphibians? You’re not alone.
Short Answer:
Believe it or not, fish are actually neither reptiles nor amphibians! They are a separate category of their own.
Because of their physical characteristics, fish can’t possibly fit into either existing category. There are many features that separate each of these categories including:
- Fin or feet
- Scales or skin
- Lungs or gills
However, some reptiles and amphibians still live in water. Both friends and foes of fish, have different abilities but share an ecosystem.
Talk about a weird neighbor.
In this article, we’ll talk about why fish aren’t considered reptiles or amphibians in-depth. We’ll also share some examples of some really cool aquatic reptiles and amphibians that are sure to give you something interesting to talk about at your next dinner party.
What Makes a Fish a Fish?
This sounds obvious, but there are a few physical characteristics that make a fish a fish. These traits are:
- Living in water
- Using fins
- Breathing through gills
- Having enamel scales
Creatures with these characteristics are considered a part of the fish category. In the same way, animals without these traits are likely not considered fish.
If it looks like a fish and smells like a fish, well… You know what they say!
Fish Live in Water
As you probably already guessed, the primary characteristic that makes a fish a fish is its ability to only live in water. Animals that are not fish normally have some sort of capability to live or survive on land, even for short periods of time.
Fish, on the other hand, die quickly on land without water! Without water to give fish oxygen through their gills, fish cannot breathe.
Fish Use Fins
Fish, unlike other types of animals, have different types of fins that help them swim through the water. These fins each have a different purpose and contribute to the fish’s ability to steer in unique ways.
For example, the dorsal fin helps the fish remain stable while swimming. The tail fin, on the other hand, helps the fish propel itself forward in the water.
Reptiles nor amphibians have fins on their body, at least not permanently. Some amphibians may hatch with fins but will eventually lose them as they grow into adulthood.
Fish Only Have Gills
Since fish only live in water, they use gills to “breathe.” Gills are small organs on the side of a fish’s body that allow it to absorb oxygen as water passes through them. (*)
Since gills function only by the passing of water, fish cannot survive on land. They don’t have lungs to be able to breathe the air.
This is why keeping your aquarium water oxygenated is so important. If your water doesn’t have enough oxygen, your fish’s gills may not be able to absorb enough into their bloodstream to stay healthy.
Using a bubbler is a great way to put more oxygen in your fish’s water to keep them happy and healthy! We recommend finding an effective bubbler suitable for your fish tank’s size if you don’t have one already.
Fish Have Enamel Scales
Fun fact:
Fish have scales made of enamel and dentine. (*)
If you don’t know what those are, they’re the same stuff our teeth are made of! I bet you didn’t expect to have something in common with a fish!
Unlike scales on other creatures, fish scales grow outwards from the fish and are able to be detached from the fish individually. They are also shiny and smooth to help the fish glide through the water and reflect light as a form of camouflage.
Camouflaging helps the fish hide from predators, so it doesn’t quickly become a bigger fish’s lunch.
While not all fish have scales, such as catfish, those that do have greater protection against predators and are able to swim much more quickly than their non-scaled counterparts.
Having enamel scales also separates fish from reptiles. While reptiles do have scales, these scales are made of keratin and are essentially a part of the animal’s skin.
Keratin is in our skin too, so you have something in common with reptiles as well!
Reptile scales are rough to protect them from scratches or bites in nature. In the case of snakes, their bottom scales are smooth to reduce friction while their side scales are rough to help them grip trees or inclines. (*)
For fish, tough, bony scales help them quickly escape predators and protect their skin and gills. In some species, such as the goby, fish may use scales as a way to attract mates. (*)
Why should a fish settle for boring grey when they could have a mate with beautiful, bright orange scales?
Why Fish Aren’t Reptiles
Reptiles have some unique characteristics that separate them from both fish and amphibians. Notably, reptiles:
- Live on land
- Only have lungs
- Have arms and legs
- Use internal fertilization
These unique characteristics give reptiles an animal category of their own. Common examples of reptiles include tortoises, lizards, and alligators.
If it has rough scales, sharp teeth, and is chasing you on land… It’s probably a reptile.
Reptiles Live on Land
Unlike fish, reptiles spend their entire lives living on land. While some reptiles may enjoy spending some time in the water (such as alligators), they do not live only in water, nor do they spend a significant amount of time there.
Reptiles are built to survive on land with their limbs, rough skin, and lungs. They thrive in sunny environments which can keep their body temperature high, since though they live on land, they are still cold-blooded.
Hotter areas of the world have more reptiles than others since they thrive in hot climates. Take this into consideration on your next tropical vacation, before you end up running into a crocodile!
Reptiles Only Have Lungs
Since they live on land, reptiles only have lungs to breathe from. Basic, I know. This is clearly different from fish, which only have gills.
Unlike amphibians, reptiles never have gills at any point during their development. They hatch on land and have lungs to breathe from the moment they leave the shell.
Reptiles Have Arms and Legs
The most obvious difference between reptiles and fish is that most reptiles have arms and legs while fish do not. Reptiles need arms and legs to travel on land, while these are not necessary for fish to swim through water.
An exception to this, of course, would be the snake, which is able to swim or travel on land without any limbs. Impressive!
Reptiles Use Internal Fertilization
Alright, to make this easy, we’ll define fertilization first. Let’s pretend we’re in science class for a minute.
Fertilization is when a sperm cell and an egg cell come together to make an embryo. That embryo then grows into a full living thing over time.
In the case of reptiles, they hatch from their eggs as babies and then grow into adulthood.
While female fish lay eggs that are later fertilized by a male fish in open water, reptiles can only fertilize their eggs using internal fertilization. This means the sperm and egg have to come together inside the female reptile’s body.
Because reptile eggs have a hard shell, unlike soft fish eggs, they are unable to be fertilized once they are already laid.
Okay, biology lesson over. But don’t take off your thinking caps before the next section!
Why Fish Aren’t Amphibians
Amphibians are often considered an enigma of the animal world. Not fully fish and not fully reptile, amphibians enjoy the best of both worlds throughout their development.
As you probably already know from that one childhood school lesson on frogs, amphibians start their lives in water and eventually develop organs to help them live on land as they grow. Because of this, amphibians:
- Can live in both land and water
- Grow limbs as they develop
- Breathe through their skin and lungs
Common examples of amphibians include salamanders and axolotls, but we find frogs to be a fan favorite.
Amphibians Live in Both Land and Water
Unlike reptiles, which mostly live on land, and unlike fish, which only live in water, amphibians enjoy a bit of both. Typically, amphibians start their lives in water and eventually leave the water once they become adults.
However, this is not always the case. Many amphibians have soft, smooth skin that can easily dry out.
If they were human, they’d need lotion. Since they’re not, they much prefer water or mucus.
We’re glad we aren’t amphibians.
As a result, many amphibians will still live near or around the water once they become an adult. This is the case for frogs, which can always be found keeping moist on a lilypad at your local pond.
Amphibians Grow Limbs
Probably the most fascinating part about amphibians is their ability to grow limbs!
While amphibians start with gills and fins to thrive in the water, they develop arms and legs as they grow.
Often, these creatures will digest their fins and tails for extra nutrients to grow their limbs. Talk about an upgrade!
Have you ever seen the difference between a tadpole and a frog? These creatures seem like night and day, and yet are the exact same organism.
Without the ability to grow limbs, amphibians would simply stay like fish their entire lives. Their arms and legs give them the ability to leave the water to find new food and habitats as adults.
Amphibians Breathe Through Skin and Lungs
Amphibians have decided they’re unsatisfied and want more than just hands and feet. Now, they want lungs too!
As amphibians develop, their gills shrink or are absorbed to make way for a healthy set of lungs. This helps them move out of the water and onto the land as they grow.
While amphibians start with gills to get oxygen from the water when they first hatch, amphibians will start breathing air through freshly-developed lungs as they near adulthood.
Some amphibians, however, are completely unique. Though they have lungs, amphibians such as the hellbender salamander and Titicaca water frog breathe mostly through their skin! (*)
Their skin is able to absorb water to take oxygen directly into their bloodstream. This also makes staying near water important for amphibians even after adulthood.
Some amphibians will also secrete a type of mucus to keep their skin moist and prevent it from drying out. If their skin gets too dry, they will essentially suffocate, as they will be unable to get oxygen into their blood.
Those of you that enjoy sunning on the beach may be thankful you aren’t an amphibian! We still are for sure.
Examples of Reptiles and Amphibians
It’s pretty clear that all these different types of animals are super cool. To give you a clearer picture of the differences between fish, reptiles, and amphibians, we’re going to show you some great examples of reptiles and amphibians.
It’s important to note that while these are big categories, not every animal fits perfectly in these categories. Some may make exceptions to rules (such as snakes not having feet), but that doesn’t mean they don’t fit in that category.
Some species just like to be complicated.
Read on to learn more about:
- Sea turtles
- Frogs
- Axolotls
Below, let us know which of these is your favorite! We love them all, though the author is partial to sea turtles.
Sea Turtles
Sea turtles, though they spend their lives in the ocean, are considered reptiles. Sea turtles use their arms and legs to coast through the water and climb up on the beach to nest.
Sea turtles have rough, protective skin on their head and limbs and a tough shell to protect their internal organs. This shell is considered their “scales,” as it is made out of hard, keratinized scutes.
Every 2-4 years, sea turtles will mate and find a beach to lay their eggs in the sand. Once the eggs hatch, baby sea turtles must fight their way to the water’s edge to begin their life in the ocean. (*)
Even as babies, sea turtles only have lungs. Because of this, they much reach the surface every few minutes to breathe.
You may wonder, how do they sleep then? When resting, sea turtles are able to snooze without breathing for up to two hours!
Though they live their entire lives with fish, they certainly aren’t one. Trust us, we checked.
Frogs
Frogs are one of the most fascinating creatures on earth. Famous amphibians, they start their lives as tiny, vulnerable tadpoles and grow into strong, bellowing frogs capable of hopping and swimming across their habitat.
As tadpoles, frogs are incredibly similar to fish. They have fins, and gills, and don’t have any limbs.
Without the ability to develop into a frog, tadpoles themselves are essentially just scaleless fish.
Rare cases of frogs that have been unable to metamorphize from tadpoles have been found. This may be due to genetic abnormalities or environmental conditions, such as a lack of response to hormones or a pond that’s just too cold. (*,*)
When healthy, frogs grow their limbs and stay in an aquatic environment to flourish in their adult lives. Staying moist and eating waterbugs is a frog’s dream!
Axolotls
Axolotls are fascinating creatures and a definite outlier in the amphibian category. Though they grow limbs and lungs, they don’t spend any of their adult life outside the water.
Axolotls also retain their gills as adults, but also have fully functioning lungs and absorb oxygen through their skin! (Unique Axolotls Names For Your Pet
An Answered Question
The next time you’re asked, “Are fish reptiles or amphibians?” You should have a clear answer to give!
Important Thing To Remember!
Fish are not reptiles nor amphibians but are in fact a separate category of their own. However, they still share some things in common with other animals, such as gills and fins with amphibians and scales with reptiles.
If you enjoyed this article, please feel free to leave a comment below and share it with your friends. Let us know what other questions you have and we may write an article on it!
