Sea Life

A Comprehensive Guide to Fish: (Characteristics, Types, and More)

A Comprehensive Guide to Fish- (Characteristics, Types and More) copy

Fishes are one of the widely known living species in the real world. They are found in every available region around the globe. These fishes are a crucial part of our ecosystem and act as a balancing factor in aquatic systems. Fishes have the ability to live in diverse living environments such as saltwater, cold water, and warm aquatic regions. These coldblooded animals are classified into vertebrates with about more than 3500+ species. This guide will inform you about the fishes, their types, and much more.

Introduction of Fishes

Fishes are an integral part of our whole biological living system. Despite having hundreds of different species, a lot of these fishes have a couple of things in common. 

These exclusive characteristics of these living beings allow them to differentiate themselves from the rest of the cold-blooded animals. Here are the 5 main characteristics most fishes have in common:

  • Being a cold-blooded animal.
  • Having no eyelids or external ears.
  • Being vertebrate animals.
  • Using gills for breathing underwater.
  • Having a two-chambered heart.

Other than these, there are multiple similarities in fishes. But, their prominent features allow them to be classified as per their:

  • Diet.
  • Shape.
  • Appearance.
  • Way of living.
  • Reproducing Method.

Evolution of Fishes

The first ever known fish (Haikouichthys), was found about 520 to 530 million years ago. The event of the Cambrian explosion, which also happened around 530 million years ago, introduced new species of fish and other cold vertebrates, thus expanding the horizon of living creatures. This expanded horizon now includes goldfish, sharks, dolphins, and tons of these aquatic living beings.

Fish Diet/Food

Fishes are classified as omnivorous, as they can easily consume plants, animals or even both, based on their species. These fishes can eat things like,

  • Plankton.
  • Algae.
  • Eggs.
  • Sea snails.
  • Worms.
  • Other fishes

And a variety of other marine life. The diet consumption rate can also be determined based on warm-water or cold-water fish. The fish in warm water generally need more food to consume than the cold water ones. It is due to their high metabolism, making them consume more food overall.

Reproduction/ Breeding

In Fish, there are male and female fishing like most living beings. There are two mechanics of breeding or laying eggs.

The first one is producing eggs in open water or sticking them to any hidden underneath, which are later fertilized by male species. Once matured, these eggs will be produced into baby larvae. The process is also called parthenogenesis.

In the 2nd Case, the fishes, instead of laying eggs, give birth to the small larvae. These will slowly mature into full-sized fishes of their particular type. 

Note: Some of the fishes eat their eggs and small babies to reduce hunger.

Types of Fishes(Based on Jaw Structure)

Typically there are 3 main types of fish, depending on the structures of their jaws.

  • Jawless Fish
  • Cartilaginous Fish 
  • Bone Fish

1: Jawless Fish (Agnatha)

These are special fishes with no proper fins. They are also lacking fish-like mouths and rather have circular mouths with teeth. They are similar to leeches and are sometimes classified as parasites. It is because agnatha can easily suck the food and nutrients from its prey. It can be divided into;

  • Hagfish
  • Lympreys

Hagfish: These fishes have elongated eel-shaped bodies, and are known to be the only fish without vertebrates but a skull. It can be of length from 1.6 to 19.7 inches. They are known for their paddle-shaped tails, which make these fishes glide through the water.


Lympreys: Lymprey originated from the Latin word lambere and petra, which means a stone licker. It is often classified as eel and has a length from 5 to 39.5 inches. They are commonly found in freshwater lakes in most of the known water bodies.

2: Cartilaginous Fish (Chondrichthyes)

These fishes do have vertebrates and a skull, but it is made of cartilage (similar to our nose and head)instead of proper bones. They are also missing the swim bladder, which simply means they continuously have to swim, otherwise, they can not survive underwater. The most common examples of these fishes are sharks and stingrays.

3: Bone Fish (Osteichthyes)

Bonefish is the most common one out of all 3 kinds. These fishes have a proper skull and a backbone. Located in all kinds of water, the fish included in this particular type are blobfish, Tuna, pufferfish, and hundreds of others. 

Types of Fishes(Based on the Habitat)

Fishes in the real world can also be classified based on the water they live and travel in. Here are all 3 types of fish (based on habitat);

Diadromous Fish

These kinds of fish are often found traveling between saltwater and freshwater. They are migratory 

.fruin and are found in areas near the ocean and rivers as it allows them to travel between both places. Most of the eel-shaped fishes including eel, salmon, and several others are included in this category.

Catadromous Fish

These fishes live in freshwater for most of their lives. Only during the season of breeding, they head towards the sea to breed. The European and North American eels are referred to as these types of fish.

Anadromous Fish

These are ocean-specific fishes that live in saltwater. They visit the freshwater only during the breeding season. Most of the salmon including pink salmon and trout fishes are common examples of anadromous fish.

Uses of Fishes

Fish is one of the widely used animals as a source of different components in different fields. Here are the main uses of fish in the real world. 

Fish as a Food Source

Since ancient times, Fish was a food source, people used to fish for them and then cooked them as food. Hundreds of dishes are being made with tons of different fish types. Caviar, one of the expensive food items, is also sourced from the fish named Sturgeon. Fishes are consumed because of all the nutrients they contain, especially Omega 3 and other good fatty acids. People around the world cook them in different styles and flavors.

Fishes as Medicine

Fishes are also being used to extract material for different medicines. It can help to lower the risks of a heart attack. Fish liver oil is also utilized to improve bone health and reduce inflammation. Fishes are being consumed for good eye care, as they contain multiple vitamins and minerals including vitamin D, zinc, phosphorus, and many more.

Miscellaneous Uses of Fish

Fish can be utilized in various ways, other than food. It is a great source of producing baby oil. People use them as feed for their pets. It is also utilized to make artificial pearls. It is being used as a major source of fish glue and many other processed fish items.

Final Thoughts

Fishes are the most beautiful and useful creatures found around the globe. They are located in every water body, with more than 3500+ species out there, these fishes are a crucial and necessary part of our ecosystem. Human beings use these fishes as their food, bonemeal, and many other useful substances. Overall, the fish are taking their part, to balance the ecosystem of our planet.

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