Is a fish a reptile?

In this post, we will answer the question “Is a fish a reptile?” and learn about reptiles general characteristics, their biology, and ecology. 

Is a fish a reptile?

No, fish are not reptiles. Reptile (from Latin, reptare, “to crawl”) is a term traditionally used to refer to a group of vertebrate animals, tetrapods, amniotes, and ectotherms, which include snakes, lizards, turtles, and crocodiles. There are currently more than 9,000 different species of reptiles spread across the planet (except at the poles).

General characteristics of reptiles

Reptiles are tetrapod animals (which have four limbs) and amniotes (whose embryos are surrounded by the amniotic membrane). They are well adapted to live in the terrestrial environment. They present thick epidermis with scales and/or osteoderms (bone deposits), which make them resistant to desiccation. In addition, some representatives lay eggs with shells that protect the embryo. All of the reptiles have internal fertilization, which prevents the desiccation of gametes.

Reptiles are ectothermic animals, that is, they are not able to maintain body temperature using their metabolism. To maintain the proper temperature, they absorb external heat, for example, exposing themselves to the sun. It is because of these characteristics that reptiles are called cold-blooded animals and are not able to live in the region of the poles.

Digestive system

The reptile digestive system is complete, starting in the mouth. Eating habits are variable, but most are carnivorous. The way to kill their prey is also different between groups. Boas, for example, kill their prey by constricting their bodies, while crocodiles use their powerful jaws. There are also those species that rely on the poison to get their food.


These animals have double, closed and incomplete circulation. The heart is divided into three chambers, the ventricle being partially divided, except for crocodilians, in which the heart is completely divided into four chambers. Although crocodilians have a heart with four cavities, oxygen-rich blood meets carbon dioxide-rich blood right after it leaves the heart, in the foramen of Panizza, the communication region between the left and right branches of the aorta.


Reptiles breathing is pulmonary, even in those species that live in the aquatic environment, such as sea turtles. They have kidneys as organs responsible for excretion, and the main product of nitrogen excretion is uric acid.


They are animals that have separate sexes, that is, there are males and females. Fertilization is internal, and most species are oviparous, and there are also ovoviviparous and viviparous representatives. The reptile egg has a limestone shell, which protects against dryness in a terrestrial environment, and four extra-embryonic membranes: allantoid, chorion, amnion, and yolk sac.

Ecological importance of reptiles

Reptiles are animals that are part of the food chain of different ecosystems. We have species, such as crocodiles and alligators, which are large carnivores, being part of the top of the chain of ecosystems where they are found.

Some species are herbivores and act as primary consumers, this being the case for some lizards. Other species, in turn, take the place of secondary consumers, such as snakes that feed on herbivores. Therefore, the extinction of some of these species, as well as their uncontrolled development, can put the balance of the ecosystem at risk.

In addition to being ecologically important, reptiles are economically important. Some of them serve as food for human beings, such as the alligator. Additionally, some species have pharmaceutical potential, such as the common jararaca venom, responsible for the development of a remedy against hypertension called captopril.

We can classify reptiles into four main orders:

– Chelonia: Among its main features, we can highlight the presence of shields and plastrons, very important structures for protection;

– Crocodilia: The animals of this order have a body covered by horny plates. They are the only reptiles that have a heart with four completely separate cavities;

– Squamata: Include representatives that have a body covered with scales;

– Rhynchocephalia: This group is considered primitive. Its body is covered with horny scales.

Are turtles reptiles or fish?

Chelonians are a group of reptiles that include turtles and tortoises. Tortoises refer to freshwater and semi-aquatic animals, as well as terrestrial animals. Turtles are those that live in the marine environment, although the term is also used for freshwater species such as the water tiger.

The most striking feature of this group is the presence of a hull. The carapace (the dorsal portion of the hoof) is formed by the fusion of the spine with the ribs. The ventral part of this shell, called the plastron, is formed mainly by dermal ossifications and, with the carapace, it forms a rigid bone structure that guarantees the protection of these animals. Another important feature of turtles is the replacement of teeth by a horny beak.

Sea turtles characteristics

Turtles are marine animals, subdivided into two families: the Cheloniidae and Dermochelyidae. In the last one, we find a single species: the leatherback turtle (Dermochelys coriacea), a name that refers to the presence of leather, instead of a shell covered by plates. In the Cheloniidae Family, we find animals with such a protective shield: hawksbill turtle (Eretmochelys imbricata), Arowana (Chelonia mydas), olive (Lepidochelys olivacea), loggerhead (Caretta caretta), flatback turtle (Natator depressus), and kemps ridley (Lepidochelys kempii).

Males and females are very similar to each other, and can be clearly distinguished only in adulthood: this is when the males have a well-developed tail and nails. 

Most of these animals are omnivorous, although some consume only food of animal origin. They are migratory and return to the beach where they were born during the breeding season, to deposit their eggs. On the coast, this period lasts from September to March; and on the oceanic islands, from January to June. Approximately two months later, the eggs begin to hatch; and the chicks leave their nests towards the water. The olive turtle reaches sexual maturity between the ages of ten and fifteen; while the others, around twenty to thirty years of life.

Although a single turtle can lay a large number of eggs, only 0.1% of the hatchlings will reach adulthood. In the first moments of their life, they are already subject to predation by birds, lizards, and crabs; and also by carnivorous animals found in the sea. As adults, they can be captured by humans, aiming to use their meat and eggs as food; and its carapace in the making of artifacts. Indirectly, pollution, habitat destruction, accumulation of plastic material in the sea, accidental fishing, among other factors, are responsible for the death of such animals, elucidating why all species have their populations in decline.


Crocodilians are reptiles that normally occupy the warmest regions of the planet and that, in general, have high rainfall or rivers, lakes, estuaries and shallow seas. They have an elongated skull, short muscular neck, extremely strong bite and a long tail. They are animals that vary in size, with species that reach almost 8 metres in length.


In this post, we answered the question “Is a fish a reptile?” and learnt about reptiles general characteristics, their biology, and ecology.

If you have any thoughts or doubts, feel free to drop us in a comment below!

Frequently Asked Questions (FAQs): Is a fish a reptile?

What were the biggest marine reptiles that ever lived in the oceans?

So far, the largest marine reptile ever discovered in Earth’s history was a member of the ichthyosaurus group, Shonisaurus looked like a cross between a whale and a dolphin. The muzzle was long, but the back was swollen and quite large.

What is the lifespan of a sea turtle?

Larger species, such as sea turtles, live between 80 and 100 years. The giant tortoise can live for over 200 years.

What is the distribution of the sea turtle?

Sea turtlers ha circumglobal geographical distribution, occurring in tropical, subtropical, and temperate Atlantic, Indian, and Pacific oceans.

What is the life cycle of sea turtles?

The life cycle of turtles and tortoises are similar: after leaving the egg, they become hatchlings, and then adult animals.

What is the most dangerous crocodile in the world?

The marine crocodile, saltwater crocodile or porous crocodile (Crocodylus porosus) is the largest reptile existing today and is extremely dangerous for humans.

Do crocodiles feed on fish?

Yes, several species of crocodiles and alligators feed on fish and they find an excellent source of energy and protein.


Vitt, L. J., & Caldwell, J. P. (2013). Herpetology: an introductory biology of amphibians and reptiles. Academic press.

Klemens, M. W. (2000). Turtle conservation. Washington, DC, 745.

Lutz, P. L., Musick, J. A., & Wyneken, J. (Eds.). (2002). The biology of sea turtles, Volume II (Vol. 2). CRC press.

Wyneken, J., Lohmann, K. J., & Musick, J. A. (Eds.). (2013). The biology of sea turtles (Vol. 3). CRC press.