Fish are the most prominent creatures of the aquatic systems. They are an important food resource for other creatures, especially for human beings. Also, the common thing in all fish is that they are cold-blooded vertebrate animals living in water.

They have scales, fins, and gills and have thousands of different species. Many fishers hunt them while many kept them as pets.

According to research, there are almost 54,711 species of vertebrate and fish are one-half of them. Also, almost 28400 species of them are in 515 families. Unfortunately, different impacts from humans like international trade and pollution has threatened many Fish species.


Scientifically collective terms for them are Agnatha, Sarcoptergii, Chondrichthyes, and Actinopterygians.

Vernacular Names

Here below some Vernacular names are given:

  • English: Fish
  • Chinese:
  • French: Poisson
  • German: Fisch
  • Italian: Pesce
  • Japanese: サーモン
  • Russian: рыба
  • Spanish: Pescado
  • Swedish: fisk


Their history on earth is more than 450 million years old and also discussed below.

Origin of Fish

About 530 million years ago after the Cambrian explosion, their evolution began. History also shows that the first fish founded was Agnatha or jawless. They come in vertebrates category and lives in a different habitat.

Fossil Records of Fish

The first bony fish fossils found in late Silurian. From early Devonian lungfishes and coelacanths were founded which are still surviving.

Distinctive Features of Fish

Fish don’t need to maintain constant internal body temperature as they are cold blooded. Environment greatly influenced their temperature. Fish having backbone and fins are the true fish, many fishes breath with gills and cover their bodies with scales.

To move up and down in the water fish uses swim bladder or air bladder. They adjust the air in their bladder and then float, this helps them to move without continuously swimming.


Fish Morphology depends on the medium they live. Fish body is divided into a head, trunk, and tail, although externally divisions could not be visible.

The skeleton in bony fish made up of bone while in cartilaginous fish it is made up of cartilage. Also, Sharks and rays are basal fishes and their skeleton made up of cartilage.

The morphology of the Fish is described below:


It is used for balance and to help move and steer through the water. There are two types of fins: Single Fins and paired fins.


It protects the fish from injuries and infections. Also, some fish have smooth and rounded edges and others have jagged and sharp.


This organ helps fish to breathe underwater. It is just behind the head on the side of the fish having tiny blooded vessels.

Life Span

There is a general assumption of people that they don’t live very long. So if you want to keep them as a Pet you should have some knowledge about different species lifespan.

They have a different lifespan from a minimum of 10 weeks to a maximum of 150 years. Also, Fishes like African Killifish and Great Barrier Reef pygmy gobies have 10 weeks lifespan. While sturgeons and scorpaenid rockfishes have 150 years.


Behavior Of Fish

Here are some common Fish behaviors that you must know just like any pet.

  • Hiding: It is one of the most common behavior and specially observed when introduced fish in a new aquarium. Usually when they feel comfortable and healthy then start coming out of hiding.
  • Swimming Erratically: Another of their observed behavior is erratic swimming. Usually when they play or exercise they swim erratically or when feeling unhealthy.
  • Fighting Fish: If you find them fighting then that means they are not feeling compatible in the aquarium. So you should do research on Fish compatibility.
  • Sitting on the Bottom: This is also the normal behavior of fishes to sit at the bottom. Many fishes like catfish spend their time at the bottom and also feed on there. Fishes also sleep at the bottom of the pond or aquarium.
  • Gasping for Air: If fish are trying to gasp Air from the top then there is water quality issue or oxygen in water is less.

Ecology & Habitat

Fishes change their ecological role throughout their lives several times. Differences between larvae and adults in some fishes are so pronounced that described as different taxa.

Gender changes among Fishes are also common, many species changes from male to female and vice versa.

Food Habits

There are four basic eating groups among fish and that are:

  • Carnivores:- They are meat-eating fish.
  • Herbivores:- Plant-eating fish.
  • Omnivores:- They can eat anything easily.
  • limnivores:- Kind of fish that is known as mud-eaters.


Their different species live in a different aquatic habitat. Bony fishes found in freshwater, brackish or sea water. Some species can tolerate salinity up to 60 ppt while some can live in less salinity.

Different species live in rocky shores, lakes, and ponds. Also, many live in kelp forests, coral reefs, rivers, and streams, under sea ice, the deep sea, fresh water, salinity water, and brackish water.

Pelagic fish lives in the open ocean, Flat Fishes lives at the bottom and Sunfish spotted at the surface of the ocean. While many fishes live in fresh water.


Fish is a water animal and consists of thousands of different species. These different species also live in different habitats like Lungfishes can live in a state of dry suspended animation.

Similarly, Antarctic fishes live in water colder than their blood freezing point. Some live in freshwater some in salinity, brackish water etc.


Taxonomy originated from Greek word taxis, meaning arrangement, and nomos, meaning law. Also, it is responsible for discovering, describing, classifying, naming and treating species. Taxonomic ranking and naming convention of Fish mentioned in below image.


There are almost 54,711 species of vertebrate and fish are one-half of them. Also, almost 28400 species of fish are in 515 families.

Fish Diversity

Fishes are such diverse animals that also could be categorized in many ways. Also, every year almost 250 new species discovered. According to FishBase 33,100 species of fish had been discovered by April 2015.

Types of Fish


  1. Gold: They are one of the fanciest aquarium fish that also live in a pond. (Scientific-Name is Carassius auratus & Life-span 30 years)
  2. Siamese Fighting: Siamese Fighting Fish is aquarium fish with a body length of 7cm. (Scientific-Name is beta splendens & Life-span 2 years)
  3. Common Carp: They found in the fresh lake and also have 2-14 KG weight. (Scientific-Name is Cyprinuscario & Life-span 47 years)
  4. Oscar: Oscar found in the United States, China, Australia, and South America. Its length is 36cm and weight 1.4kg. (Scientific-Name is Astronotusoscellatus & Life-span 10-13 years)
  5. Wels Catfish: Found in basins of Baltic, black and Caspian sea. Its length is 4m and weight 400 Kg maximum. (Scientific-Name is Silurusglanis & Life-span 60 years)
  6. Zander: Found in the Aral Sea and Lake Constance. (Scientific-Name is Sander Lucioperca & Mass of the body is 20KG)
  7. European Seabass: Live in Fresh and brackish water and also known as Sea Dance. (Scientific-Name is Dicentrarchuslabrax & Life-span 25 years)
  8. Northern Pike: Considered a symbol of North Dakota, also founded in Fort Peck Lake, Lake George, Lake of Woods. ( Scientific-Name is Pike & Life-span 7 years)
  9. Sword: Also found in tropical and temperate part of the Indian Oceans, Atlantic Ocean and Pacific Oceans. (Scientific-Name is Xiphias gladius & Life-span 9 years)
  10. Atlantic Cod: Found in the Bay of Biscay, also having mass 96KG. (Scientific-Name is Gadusmorhua & Life-span 25 years)
  11. Ocean Sun: Heaviest bony fish in the World, also swim 26KM per day. (Scientific-Name is Molamola & Life-span 10 years)
  12. Doctor: Used in a spa treatment for the skin patients. Founded in river basins of Turkey, Iran, Iraq, Oman, and Northern Syrian part. (Scientific-Name is Garrarufa & Life-span 6-7 years)
  13. Zebra: Lives in fresh water and is also a popular aquarium fish. (Scientific-Name is Danio rerio & Life-span 5.5 years)
  14. Neon Tetra: They belongs to the characin family and founded countries like Peru and Brazil etc. (Scientific-Name is Paracheirodon & Life-span 5 years)
  15. Nile Tilapia: Found in Victoria Lake, length is 60cm and weighs 4.3KG. (Scientific-Name is Oreochromis Niloticus & Life-span 9 years)

Fish Fun Facts

These are some fun facts about them:


Apart from these, there are many other fun facts like many of them could fly, a few can also feel pain like other mammals.



Azka Hassan

A software engineering graduate from UET Taxila, I started my carrier as an SQA engineer in the year 2013 and have worked as a Quality Assurance Engineer and Content Creator at various organizations. Currently working as a Content Manager at Tapedaily. Writing research-based content related to Plants, Animals, and various kingdoms are my key interest.

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