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Last updated date: 19th Apr 2024
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Know in Details about Types of Fish and their Characteristics 

Fishes have been on this planet for a very long time and they date back to about 450 million years. These organisms are gill-bearing and have to live in an aquatic environment in order to survive and reproduce. These organisms are mostly craniates and don’t have limbs that are provided with digits. Fishes tend to form a particular sister group known as tunicates and together they tend to form olfactores. In these notes, students will get to know about types of fish and other definitions of their physical characteristics, and much more. There is simply not a single speck of doubt that all of their questions will be answered in this particular segment for sure. 

In the present time, there are more than 31,000 different species of fishes present on the planet. There are many different environmental conditions that have led to the changes that have been made in fishes and made their evolution process a little bit more interesting. Also, there are certain other factors such as seabed morphology, depths, current well as the temperature and salinity of the water conditions. Many of the different species of fishes have adapted to their environment. With the help of our notes, students will be able to learn more about the fish body parts and how they perform different functions. 

Description and Anatomy of Fish: Parts of a Fish 

One of the most important things to know about the fishes is that unlike mammals, they are mostly cold-blooded or ectothermic. So, that would mean they do not have the need to maintain their internal body temperature in a constant manner. To be very honest, the temperature of the body of a fish mostly gets influenced by the environment that they are in. In these notes, we are going to learn about parts of a fish and much more. The fishes always have a backbone and some fins. There are gills present in the body of the fish which helps them in the process of respiration. There are also some scales present in order to provide a proper cover for their body. It is a belief amongst researchers that fishes began their process of evolution more than 400 million years ago. To this day, we have more than 31,000 different species of fish that have been discovered and some of them are not even on the verge of discovery. It is not really a surprising fact since the water world is so large that so much more remains to be discovered. For those who need fish information, these notes are very useful. 

The fins present in the fish are one of the most important body parts of a fish for sure. These fins are mostly used in order to offer some balance to the body. It is also a very important factor in the steering and propelling of the fish in the water. The fishes mostly have 2 different types of fins for sure. There are some single fins that are mostly situated in the centerline of the body which is the top and the bottom part of the body. There are also paired fins that are present in the body of a fish. The tail fin or the caudal fin is the one fin that is main and is useful in moving the body of a fish forward when they are swimming in the water. The anal or the dorsal fins which are situated in the top parts and the bottom parts are mostly used for keeping the balance of the fish in the best way. Without the presence of the dorsal fins, the fish might roll over. The main function of the paired fins is to ensure that the hovering and steering happens in a proper way without any hassle. So, it can be said without a shadow of a doubt that these fins are one of the crucial fish body parts.

The exterior of a fish has a certain type of layering that is made up of scales. These scales tend to have an overlapping effect with one on top of another. The main function of these scales is for the protection of the fish against certain infections and injuries in the water body. There are some important species of fish that do not have scales present in their bodies. One of the main examples of a fish like that is the Puffer Fish. One important fact about these fish body parts is that the scales tend to be pretty sharp and jagged as well. This is due to the fact that it acts as a protection for the skin. With the mucus traps present on the scales, it can help in immobilizing bacteria and certain viruses as well. Hence, there are no harmful materials entering the body of the fish due to the presence of scales. Also, the scales help in providing a bit of friction into the body, and hence with these scales, fishes are able to move freely in the water bodies without any trouble. 

For the respiration process underwater, fishes have a very specific set of organs that are known as gills. These gills are the main parts of a fish that help them in breathing underwater without any hassle. The gills are situated behind the head of the fish just at the side. Gills have thousands of different capillaries which are more commonly known as blood vessels. The water that is pumped through the gills will enter the body of the fish after the oxygen has been filtered out of the water. This reaches the blood of the fish and hence helps in respiration. There is a certain cover present on the gills which is known as the operculum. The structure of the operculum is pretty much similar to a bony plate that is also very flexible in nature. The gills are very sensitive and hence need protection which is why the operculum exists in the body of the fish. It can be said that it is one of the most essential parts of a fish as it helps keep the gills safe from sensitive injuries as well. Apart from respiration, gills also have a very important role to place when it comes to the excretion of certain waste products that include ammonia. Ammonia is extracted from the bloodstream of a fish with the help of gills. 

Another one of the most important characteristics of fish is that they have an air bladder or swim bladder. This is mostly found situated in the fish’s abdomen area. This is the one body part of the fish that helps in the movement of the fish upwards or downwards in the water body. With the adjustment of the air amount present in this bladder, fishes are able to make adjustments to the depths at with they will be moving in the water.

There are so many different types of fishes that are able to see colors and that means some of them to have excellent vision for sure. Also, there are certain nostrils present in the fish which are very helpful when it comes to the detection of certain smells and odors in the water bodies. While there are some types of fish that have rows of teeth, there are some that don’t. This is totally dependent on the species that they belong to. Another one of the most important organs in a fish would include the lateral line which is situated right on the side of the body. The lateral line consists of sensory hairs and the main function of these hairs is to detect certain vibrations that occur underwater and to determine the source of the vibration. It can also be said that fishes are able to travel under the murky water and low light due to the presence of lateral line in their body.

We have some very important details about fish that students would definitely find very useful. With the help of these notes, students will not only be familiar with the species of fish but they will also be able to learn certain facts about the animal that help them in getting a better understanding of the species in the best way. 

Classification of Fishes

Fishes belong to the Class Pisces and they can be further classified into 3 different categories. The Fish classification sorts fishes into: 

  • Osteichthyes

  • Placodermi (Aphstohyoids)

  • Chondrichthyes


These fish are found in marine water, freshwater, or brackish water.

These are basically the types of Pisces that are found mostly in freshwater, marine water, or brackish water. There are some important characteristics present in these types of fishes that make them perfectly fit this particular category and we are going to learn about it right here. According to the taxonomists, these fishes tend to have a very bony endoskeleton. Also, these fishes have the jaw suspension that is autosylic in nature. There is an absence of claspers in the body of these fishers. Also, these fishes have gills that are mostly covered by the operculum which is a bony plate that helps in the protection of the fishes in the best way. Most of the fishes in this particular category tend to have air bladders that are present for the movement of the fish. The types of fish that belong to this category are the ones that can be further classified into certain groups such as Crossopterygii and Actinopterygii. 

Placodermi (Aphstohyoids)

When it comes to this particular classification of fishes, there is a fact that is not known to many. The fishes that belong to this particular category are the ones that are pretty much extinct in this group. The fishes had an exoskeleton that was created in the form of certain shields for the protection of the fish. Also, the endoskeleton present in these organisms was very bony. The jaw suspension of these fishes was autodiastylic in nature. Most species from this category survived until the Devonian period came to an end. The organisms belonging to this particular category also has a heterocercal Caudal fin present in their body. Some of the main examples of Placodermi are Climatius and Bothriolepis. 


These types of fish are mostly situated in the marine environment as they require that type of environment in order to survive and extend their line. These fishes contain an exoskeleton that mostly resembles the placoid scales. There is also a presence of an endoskeleton that is mostly cartilaginous. These fishes tend to have an anphistylic jaw suspension. The gills that are present in the body tend to act as certain respiratory organs. Not to mention that the caudal fin is present in these fishes and that it is heterocercal. There are also claspers present that act as the reproductive organs for the male species. However, Chondrichthyes do not possess air bladders. This particular category of fishes is mostly divided into two categories such as Bradyodonti and Selachi. Some of the main examples of this category include Scoliodon and Heteroloatas. 

FAQs on Fish

1. Why Do Fishes Die When Taken Out of Water? 

One of the main reasons why do fishes die when taken out of water is that their respiratory organs, known as gills, are created specifically to ensure that they are able to breathe under the water. These gills are rendered useless outside of the water and hence aren’t able to help fishes breathe.

2. What is the Scientific Name of Fish? 

There are different species and each of them has different scientific names. Hence, there is not one particular scientific name of fish as it totally depends on the fishes. For example, the scientific name of Rohu fish is Labeo Rohita.

3. What is the Function of the Operculum? 

An operculum is a bony plate designed to provide protection to the gills of the fishes so that there is no external injury harming them. This structure is present in most fishes except some that don’t have them. 

4. Name the Different Categories of Fish Classification.

The different categories of fishes include Osteichthyes, Placodermi (Aphstohyoids) and Chondrichthyes