How many species of fish are there in the world?

In this post, we will answer the question “How many species of fish are there in the world?”. We will explore the number of fish species present on our planet and understand a little about the diversity of this group of animals.

How many species of fish are there in the world?

It is estimated that there are currently around 32,000 living species of fish in the world. Currently, one of the most valued fish in the world is the Bluefin Tuna, which can measure up to five meters and weigh up to 680 kilograms.

There are many, it is true, but as we have said, this number increases from time to time, due to the new species that are discovered. To this number, we must add that it is divided into 400 different families.

Furthermore, the 400 Families are divided, in turn, into two classes and two subclasses each. These categories are made, of course, so that all species are classified, as this helps a lot in future research. Let’s do more numbers. Of the 32,000 known species, 8% or a total of around 2,500 can be kept as ornamental fish. 

Fish concept and species concept

Fish have many characteristics that distinguish them from the rest of the inhabitants of planet Earth. One of them, which is perhaps the most prominent, is that they are one of the oldest vertebrates.

Specifically, when we speak of fish, we are referring to “the vertebrate animal of simple circulation, endowed with fins, with the body generally covered with scales, which breaths through its gills, and reproduces through its eggs”.

As mentioned above, within the group we call “fish”, various divisions or subgroups can be made. Yes, we may have often heard about species, but… do we know what a species is? We will explain it to you below.

A species, this time a biological species, is the set of organisms or natural populations capable of interbreeding and producing fertile offspring, but cannot do so with members that belong to other species.


Fish are found in the most varied aquatic environments and are characterized by being the most numerous and diverse group of vertebrates. In this group of animals, we have representatives with a typically fusiform body; breathing, usually of the gill type; the presence of fins; and ectothermic. This group includes cartilaginous fish, which have a skeleton formed by cartilage, and bony fish, which have a bony skeleton.

It is noteworthy that many changes occurred in the classification of animals after adopting the cladistic methodology and improving DNA analysis techniques. Recent studies demonstrate, for example, the monophyleticism of the Agnatha (Jawless fish) and the Chondrichthyes (Cartilaginous fish), but not that of the Osteichthyes (Bony fish), which is a paraphyletic group.

Jawless fish

Lampreys, to give you an idea, are very, very similar to eels when considering their body shape. Of course, they are not closely related to each other. They have an elongated gelatinous body with a cylindrical shape. Their skin is scaly and slimy and slippery. They can inhabit both salt and fresh water and reproduce through eggs.

Hagfish are among the oldest vertebrates on the planet. These fish are very strange creatures. Its body is long and, as in the case of lampreys, it is completely covered with a gelatinous, sticky substance, etc. In the absence of jaws, they have developed a pair of structures located in the outer area of ​​the mouth that allows them to capture their prey. Furthermore, on several occasions, they enter the organism of other living animals, which gnaw and devour their entrails thanks to a protruding, jagged tongue. However, this practice is usually not common, as they usually eat meat from dead animals. They live at the bottom of the sea, where light is scarce, which has played a key role in the poor development of their senses.

Cartilaginous fish

The main characteristic of Cartilaginous fish is that their skeleton is not bony, but formed by cartilaginous structures. They are also remarkable for having external gill crevices. Cartilaginous fish are sharks, rays and chimeras.

Sharks are one of the strongest predators in the animal kingdom. They did not change much in terms of morphology throughout time, so it can be said that they remained virtually immune over time.

Stingrays share many characteristics in common with sharks. They are distinguished from them mainly by having a body arranged in a ventral position adopting a flat shape.

Lastly, we find the Chimeras. These fish are one of the rarest and oldest animals in existence. Today, few species of chimera survive. To give you an idea, in terms of shape, they walk halfway between sharks and rays. They are often nicknamed ratfish and they live in deep seawater.

Bony fish

Of all the species of fish that exist, those under the bony fish classification are the most common and the ones we are most used to.

Bony fish, as the name suggests, have a bony skeleton. In these animals, the gills are covered by the operculum, a kind of bony flap that protects these structures. In bony fish, the presence of the swim bladder is observed. Other characteristics that can be mentioned are mouth at the anterior extremity, intestine ending in anus and ammonia excretion.

Based on their fins, bony fish can be distinguished between Actinopterygian fish and Sarcopterygian fish.

Actinopterygian fish are bony fish whose fins are endowed with structures called rays. Sarcopterygian fish are bony fish with lobed fins.


In this post, we answered the question “How many species of fish are there in the world?”. We explored the number of fish species present on our planet and understood a little about the diversity of this group of animals.

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

Frequently Asked Questions (FAQs): How many species of fish are there in the world?

How many fish are in the world?

There are trillions of fish swimming out there, around 3.5 trillion! And they come in all shapes, sizes, and colours, and they live in very different places too, at different temperatures and depths. Scientists say that all of the world’s water bodies are home to 32,000 species of fish.

How do species of fish are discovered?

Scientists in the fields of taxonomy work a lot to describe species for science every day.

How do deep-sea fish live?

These fish live in a zone called the Abyssal zone. There are no algae there. Therefore, most abyssal fish species are carnivorous and have large, scary teeth. Sunlight does not reach these deep regions, where the temperature is between 0 and 4 degrees Celsius. Despite all this difficulty, there is a great diversity of species living in extremely deep environments.

Which fish species is considered the king of fish?

The fish species commonly called the “king of fish” is the Salmon.

What is the biggest fish in the sea?

The whale shark (Rhincodon typus) is the biggest fish species in the sea. The whale shark is a filter-feeding species. They are the remaining living member of the Rhincodontidae family.

Are there more fish in the ocean than stars in the sky?

The answer is not so simple, but we know that each day it is necessary to study more and more the biological diversity of our planet. There are thousands of species to be described. We only know 20% of the ocean!

What is a leather fish?

The term leather fish is the common designation to certain teleost, siluriform fish which have a scaleless body. Such fish are represented by some catfish and husks, among others.


Helfman, G., Collette, B. B., Facey, D. E., & Bowen, B. W. (2009). The diversity of fishes: biology, evolution, and ecology. John Wiley & Sons.

Harrel, R. C., Davis, B. J., & Dorris, T. C. (1967). Stream order and species diversity of fishes in an intermittent Oklahoma stream. American Midland Naturalist, 428-436.

Wilson, J. M., & Castro, L. F. C. (2010). Morphological diversity of the gastrointestinal tract in fishes. In Fish physiology (Vol. 30, pp. 1-55). Academic Press.