Are Fish Reptiles? Animal Difference Simplified For Kids

All the animals in the world are classified into different groups, and animals with similar features are grouped under a particular class.

Among vertebrates (phylum Chordata), the animals with backbones, there are five well-recognized classes of animals. These vertebrate classes include mammals, amphibians, reptiles, fish, and birds. Fish is an animal class and comprises as many as 34,000 species that live in fresh and saline waters worldwide.

Mammals are animals that have hair on their body and drink their mother's milk as babies. Birds are animals with feathers. Amphibians are born in water. They have gills as babies but develop lungs as they grow up. Reptiles are animals with scaly skin and are born on land. Fish belong to the phylum Chordata and are characterized by gills on their body for breathing and fins for mobility. They are fully aquatic and live only in water. They are vertebrates with a developed spine. They are ectothermic - which means they are cold-blooded. Their body temperature varies as per their ambient environment. However, some exceptions, like the shark and the tuna fish, are warm-blooded and maintain a high body temperature. Fish are known to communicate with each other acoustically regarding courting, predators, and food.

If you would like to explore more information on fish, do check our articles on goldtail angelfish facts and are fish omnivores?

Is a fish considered a reptile?

Fish are considered animals, but they are not reptiles. Specific characteristics need to be met for an organism to be classified as an animal. Typically, animals have multiple cells; they consume food for energy, react to stimuli, reproduce sexually, and are mobile.

Since fish ticks the criteria on all accounts, it is generally accepted that fish are animals. Fish is a class in itself in the animal kingdom. Fish are categorized into three main subcategories, namely jawless fish, bony fish, and cartilaginous fish. Lampreys and hagfishes are jawless varieties of fish. Ocean sunfish, tuna, and salmon are some examples of bony fish, while skates, sharks, and rays are cartilaginous fish.

Fish are unique creatures. There are more fish species than all other vertebrate animal groups combined with amphibians, mammals, birds, and reptiles. Fish differ from other animals because they are characterized by gills, scales, and fins and live only in water. Different animals live in water too, and some amphibians, like a frog, are known to have gills as babies. However, they do not qualify as fish.

Do you know jellyfish, starfish, whales, and dolphins do not belong to the class of fish? Jellyfish and starfish are invertebrates, while whales and dolphins might seem to qualify as fish but are actually mammals. On the other hand, sea horses, eels, and sharks are fish.

Is there an evolutionary link between fish and reptiles?

As per the theory of evolution, species of other vertebrate classes of animals like birds, amphibians, mammals, and reptiles developed after fish. It is generally accepted that fish was one of the earliest prominent marine animals. It gradually evolved in the Paleozoic era to form diverse varieties.

Fish eventually went through further evolution, and reptiles came into being. One of the supporting evidence to this is the structure of the heart of fish and reptiles. The heart of a fish has only two chambers, while the hearts of reptiles are more evolved and have three chambers.

Do you know fish cannot typically swim upside down? The reason for this is likely evolutionary. If swimming upside down doesn't have an advantage for the fish, it doesn't evolve to learn it. Scientists believe that there are certain benefits for fish to swim with their tops up - it helps in the blood circulation from the brain to the heart. Also, with their eyes located on the dorsal side, they can look out for food and predators. Fish are top-heavy, so swimming with the dorsal side of their bodies up also aids in mobility.

Why is a fish not a reptile?

We understand that fish and reptiles are two different animal classes. Many characteristics set these two classes of animal kingdom apart.

The first is that a fish is an aquatic animal that lives only in water- both fresh and seawater, while a reptile can live in water or land.

Fish are ectothermic, which means they are cold-blooded; their body temperature is dependent on their surrounding temperature. Reptiles are also cold-blooded and have their body covered by scales or scutes. All fish have scales, except for those that fall in the cartilaginous category. Fish have fins that help them swim, while reptiles have tiny legs as limbs for mobility, and in the case of snakes, it is scales. Some examples of reptiles are crocodiles, alligators, and snakes - they can be found in both land and water. Chameleons and lizards are also reptiles that live on land.

The reproduction in fish happens through the external fertilization of eggs. They lay eggs in water which the male fertilizes. On the other hand, the reptile eggs are internally fertilized. Reptiles usually lay eggs on land, their eggs are amniotic, and hence they survive on land. Fish breathe oxygen in water with the help of gills. Gills comprise thread-like structures called filaments. Fish take air from the water through their mouth and exhale through gills. Reptiles, on the other hand, have lungs for respiration. Their skulls have nasal openings that help them to breathe in and out.

What is the key difference between a fish and a reptile?

There is not one key differentiating factor between a fish and a reptile, but many. These differences are related to their habitat, reproduction, respiration, skin, and locomotion.

Fish live only in water, while reptiles can live in both land and water. Most reptiles are oviparous, which means their newborns hatch from eggs that are fertilized inside the body. Some reptiles give birth to live newborns. In almost all types of fish, with a few exceptions, the eggs are fertilized externally.

Reptiles have a well-developed respiratory system; they breathe air through their lungs and cannot breathe underwater. One exception to this is are turtles. Fish breathe through gills. Fish use their fins for swimming, while most reptiles have small limbs for movement. Reptiles like snakes use their body scales for movement. The skin of reptiles is scaly and tough. Their epidermis is water-tight, which makes survival in a land environment possible. Most fish, on the other hand, have scales for skin.

Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for are fish reptiles? animal difference simplified for kids, then why not take a look at burrowing animals: fascinating facts on hole gophers for kids, or purrrfect facts about the ragamuffin cat kids will love?