Are Fish Reptiles?

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Everybody knows that our rivers and oceans are home to some of the longest-existing creatures on this planet. Crocodiles, sharks, and jellyfish are three examples of species dating back millions of years, when reptiles were the dominant species on earth.

shark in shallow water

Along with their long existence, fish and reptiles share something else in common: they’re both cold blooded. But does this mean that reptiles and fish are one in the same? This blog post will answer this question and provide more details on what makes fish different from reptiles and amphibians

Are Fish Considered Reptiles?

No, fish are not considered reptiles. They’re not considered amphibians either. In fact, fish are their own classification with thousands of different species in its genus. 

Many people accidentally assume that fish can be classified as reptiles because they are cold-blooded vertebrates that have been around for millions of years. However, this simple comparison in no way makes them the same. In fact, there are many important differences between fish and reptiles. 

What Is the Difference Between Fish and Reptiles?

Fish and reptiles are both members of the animal kingdom, but they belong to different classes and exhibit distinct characteristics and adaptations. The primary differences between fish and reptiles lie in their anatomical structures, reproductive strategies, and modes of respiration.


Fish are aquatic vertebrates that have streamlined bodies and are adapted for life in water. They possess fins, gills, and scales. Fins help fish maintain balance and maneuver in the water, while gills extract oxygen from water, allowing fish to respire. Fish also have a swim bladder, an air-filled sac that helps them control buoyancy.

Reptiles, on the other hand, are terrestrial or semi-aquatic vertebrates. They have limbs with claws, dry scaly skin, and lungs for respiration. Reptiles have well-developed skeletal systems that enable them to move on land efficiently. They lack fins and scales like fish.


Fish exhibit various reproductive strategies. Most fish lay eggs, and their eggs are fertilized externally, outside the female’s body. Some fish, such as sharks and rays, give birth to live young, a process known as viviparity. They possess specialized structures for internal fertilization. Additionally, some fish, like some species of tilapia, exhibit parental care by guarding their eggs and young.

Reptiles have diverse reproductive strategies as well. Most reptiles lay amniotic eggs covered by a leathery or calcified shell. The eggs are fertilized internally through copulation. Reptiles are known for their temperature-dependent sex determination, where the temperature during incubation determines the sex of the offspring. While most reptiles lay eggs, a few species, such as some snakes and lizards, give birth to live young.


Fish primarily respire through gills. Their gills extract oxygen from water as it flows over them, allowing fish to extract dissolved oxygen for respiration. This adaptation suits their aquatic lifestyle.

Reptiles are air-breathing animals and possess lungs. They rely on lungs for respiration and have evolved more efficient respiratory systems to adapt to life on land. While some reptiles, like turtles and tortoises, can hold their breath for extended periods, they still require oxygen-rich air to survive.

Habitat and Behavior

Fish are found in various aquatic habitats, including freshwater and saltwater environments. They are well-suited for life in water, with adaptations like streamlined bodies, fins for propulsion, and gills for extracting oxygen. Fish exhibit diverse behaviors, such as schooling, migratory patterns, and various feeding strategies.

Reptiles occupy a wide range of habitats, including deserts, forests, grasslands, and aquatic ecosystems. Their adaptations allow them to tolerate different climatic conditions. Reptiles are ectothermic, meaning they rely on external heat sources to regulate their body temperature. They exhibit diverse behaviors, such as basking in the sun, burrowing, and hunting.

Classifications of Fish

Fish can be classified into various categories based on different criteria. Here are some common classifications of fish:

  • Jawless Fish:
    • Agnatha: This group includes lampreys and hagfish. They lack jaws and paired fins.
  • Cartilaginous Fish:
    • Chondrichthyes: This group consists of sharks, rays, and skates. They have skeletons made of cartilage instead of bone.
  • Bony Fish:
    • Osteichthyes: This is the largest group of fish and includes most familiar fish species. They have skeletons made of bone.
  • Ray-finned Fish:
    • Actinopterygii: This group comprises the majority of bony fish species. Their fins are supported by bony rays.
  • Lobe-finned Fish:
    • Sarcopterygii: This group includes coelacanths and lungfish. They have fleshy, lobed fins.
  • Freshwater Fish:
    • Fish that inhabit freshwater environments, such as rivers, lakes, and ponds. Examples include trout, catfish, and tilapia.
  • Saltwater Fish:
    • Fish that live in marine environments, such as oceans and seas. Examples include tuna, cod, and clownfish.
  • Anadromous Fish:
    • Fish that migrate from saltwater to freshwater to reproduce. Examples include salmon and sturgeon.
  • Catadromous Fish:
    • Fish that migrate from freshwater to saltwater to reproduce. Examples include eels and mullets.
  • Demersal Fish:
    • Fish that live and feed near the bottom of aquatic environments. Examples include flounder, halibut, and catfish.
  • Pelagic Fish:
    • Fish that live and feed in the open water away from the bottom. Examples include tuna, mackerel, and marlin.
  • Herbivorous Fish:
    • Fish that primarily feed on plants and algae. Examples include certain species of carp and tangs.
  • Carnivorous Fish:
    • Fish that primarily feed on other animals. Examples include pike, barracuda, and groupers.
  • Deep-sea Fish:
    • Fish that inhabit the depths of the ocean. They are adapted to withstand extreme pressure and low light conditions. Examples include anglerfish, gulper eels, and dragonfish.

These are just some of the many classifications of fish, and there are numerous species within each category. Fish exhibit a remarkable diversity of forms, habitats, and adaptations, making them a fascinating group of animals.

Wrapping Up: Are Fish Reptiles, Amphibians, or Something Else?

Much like the differences that set apart reptiles and amphibians, fish also have many differences that make them neither a reptile or amphibian. However, they do share a lot in common with them.

The easiest way to remember the difference is that fish are equipped to spend their entire lives in water, as where reptiles are more versatile with the environments they can inhabit.

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