Skip to main content
  1. Home
  2. Other animals

PawTracks may earn a commission when you buy through links on our site.

What’s the difference between fish and reptiles? The one key difference

Rebekkah Adams
By

There are many species in the animal kingdom, likely between 7 and 8 million in total. That means we share this Earth with countless others, most of whom look nothing like us (even though we’re fairly closely related in the grand scheme of things). Our nearest relatives are other vertebrates with backbones, like fish, reptiles, amphibians, mammals, and birds. So, what separates humans from frogs, or turtles from sharks? While these creatures do have some fundamentals in common, there are a number of characteristics that set each species apart. Knowing the difference between fish and reptiles will give you a better understanding of the natural world and your pets. 

Sea turtle swims next to fish in tropical water
Image used with permission by copyright holder

Are fish mammals or reptiles?

Actually, neither! It may be surprising to learn that fish are their own thing—more specifically, their own class. While humans, dogs, and even platypuses all belong to the mammal group, fish and reptiles each have unique traits that make them special. Most notably, mammals and birds are warm-blooded, while fish, reptiles, and amphibians are cold-blooded. That’s not where the similarities and differences end, though. 

Recommended Videos

How are fish, reptiles, and amphibians alike?

All of these creatures are ectotherms, or cold-blooded, which means they can’t produce their own heat. While our body temperatures stay at relatively the same level regardless of the weather, body temps for this crew fluctuate to reflect their environment. That’s why you need to keep it really warm in the cage for your bearded dragon or boa constrictor—reptiles frequently slip into hibernation when it gets too cold. You’ll also notice that none of these animals have feathers or fur. We need that layer to trap in the heat that we generate, but that would be counterproductive for a fish that gets its heat from the water.

How are fish, reptiles, and amphibians different?

For starters, each has a slightly different breathing system adapted for the habitat they live in. Fish live entirely underwater and breathe through gills (though a few noteworthy lungfish are able to breathe air). They’re also covered in scales and have fins instead of feet, all of which are designed to help streamline their swimming. Altogether, from head to tail, fish are meant to live their whole lives under the sea.

Then you have reptiles, which can live nearly their whole lives in the water, like a sea turtle. These animals only emerge to lay eggs on land. Unlike fish and amphibians, they have their babies on land, even if they’re water-dwelling. A few reptiles, such as desert snakes, have very little contact with water at all. That’s why almost all reptiles have thicker, scaly skin that’s not as suited to living underwater full time.

Amphibians fit in the middle because they spend the first part of their existence in the water with gills but then spend their adult life breathing air with lungs. Think about the way a tadpole transforms into an adult frog and you’ll understand what we mean.

Seahorse curls his tail under the water
Image used with permission by copyright holder

What do I need to know to take care of my reptile or fish?

Reptiles run the gamut of care and habitats. A turtle is very different from a snake, and both are very different from a crocodile. Because of this, your new pet will have very specific needs that vary greatly depending on the type of animal. Many lizards, turtles, tortoises, and even some snakes need lots of moisture, so some require constant misting or a bowl. Aquatic turtles spend nearly their whole lives in the water and only come up to bask and warm themselves. 

Most of us have a picture of what a fish looks like, but there are other animals that fit into this category, like seahorses and rays. Nearly all fish will want a full tank with plants and wonderful accessories. But just because they can breathe underwater doesn’t mean they don’t need oxygen—they do, and in spades. Make sure your filter provides enough fresh air to sustain all the life in your tank. 

You might look at a bearded dragon and then at your betta fish and not see a lot of similarities, but they actually have plenty in common. One key factor in all this is to keep your enclosures warm since your reptile or fish can’t generate their own heat. Otherwise, you might come to find them in a deep sleep if it gets cold. We recommend a thermometer and hygrometer for all the tanks you run. And all pet ownership requires dedication, love, and care for the beautiful creature who’s been entrusted to your care.

Editors' Recommendations

Topics
Rebekkah Adams
Rebekkah Adams
Contributor
Rebekkah’s been a writer and editor for more than 10 years, both in print and digital. In addition to writing about pets…
Check these 3 things immediately if you have fish swimming at the top of the tank
Here's what might be causing fish to swim on the top of their home
Fish swim around in a tank with a bubbler

Before you set up your first tank, you likely didn't realize how much work went into maintaining the perfect ecosystem. In nature, we have the checks and balances of evolution to guide the delicate balance, but in an aquarium, it's just you. Learning how to clean, feed, and decorate takes time and research but will certainly benefit you — and your swimmers — in the end. Since fish can't tell you what they feel or even bark to let you know they need something, you'll discover other cues that tell you something's up. If you find your fish swimming at the top of the tank, take action right away. Here's what to do when your fish spend too much time at the surface.
What does it mean when your fish swim to the top?
Usually, your fish go to the surface when they're not getting enough oxygen. Unlike you, fish use their gills to breathe the air that's already in the water. However, in some circumstances, there's not enough oxygen in the tank for all the fish to breathe easily. To combat this, they swim up to the surface, where there is oxygen-rich water. You may notice some gasping or other signs that they're not well while they are up there. 

How do you oxygenate a fish tank?
The basic solution is to keep your tank oxygen rich and also low in CO2. You can do this by moving the water a bit more with an air pump or fan, which exposes the liquid to the air and helps get it ready for easy breathing. Be careful not to negatively impact other factors like temperature (more on that in a bit). Whatever you decide, make sure you have a long-term solution in place or the fish will go right back to the top again.

Read more
What you need to know about sugar gliders before you get an exotic pet
Follow these steps to set your sugar glider up for success
Sugar glider clings to their owner's thumb

Choosing a small pet involves almost as much deliberation as selecting a breed of dog. While there are a lot of factors to take into account, a sugar glider might turn out to be the perfect fit with their curious personality, attachment to your family, and fondness for pockets.

Like any exotic pet, gliders require expert care plus some dedicated research to choose the right breeder or pet store. But with the right prep, your new mammal will fit in perfectly and bond with the whole family. Keep reading to find out if sugar gliders are good pets.
What are sugar gliders?
Unlike most little pets, sugar gliders aren't rodents but marsupials. This gives you a few distinct advantages, as they behave differently from hamsters, guinea pigs, or gerbils. For starters, these are highly social creatures and they will bond with every member of the family and even other pets in the house. Because gliders don't smell like the animals your cats and dogs like to chase — rats, gophers, and bunnies, to name a few — many bigger pets can get along with your new friend. You'll need to introduce them carefully, but they can form lifelong attachments to each other.

Read more
Can you make a profit breeding your bearded dragon?
Does breeding your bearded dragon make you money? Read on to find out
Two bearded dragons sit on a rock

The first step in getting a new pet of any species is research. You want to make sure you're adopting or purchasing your pet from a reputable breeder who uses ethical sourcing techniques to acquire their animals. While veterinarians suggest that all pet parents spay and neuter their companions, some animals can be bred without causing distress to you or your pet.

One of the easiest pets to breed is the bearded dragon. With that being said, we recommend having experience under your belt before you embark on your journey as a breeder. Here's what you should know about breeding bearded dragons.
Is my beardie male or female?
When they're babies, it's really difficult to tell the sex of your lizard. Wait until he or she reaches maturity before making that determination, which is actually a good thing for breeding. You don't want to start your female reptile before 18 months for health reasons. In order to look at the little beast, you need to get comfortable enough to feel the underbelly, so give it a few days after bringing your beardie home.

Read more