Aquarium Anecdote – Fun Facts About Fish

Fish are the oldest inhabitants of the earth. Their long history makes them very interesting and full of facts. Therefore, researchers and enthusiasts are always curious to know these facts about fish. For example, many want to know how many fish are in the ocean. In such a way, many are curious about types, distribution, etc. The answers to these questions and many other fish facts are in this article.

how many fish are in the ocean

Fish Types in the World

There are more than 34,500 fish species around the world. Still, the number is increasing over time. There are three main groups of fish, which are the following.

Jawless Fish

As the name suggests, they lack jaws but have a backbone. They appear like eels and use their tongue to eat food. Lampreys and hagfish are the only remaining species from this group.

Cartilaginous Fishes

Cartilaginous fish are the oldest jawed vertebrates. Their skeleton is built with cartilage. Following are the specific characteristics of this group.

Paired fins and nostrils Two-chambered hearts
Movable jaws with well-developed teeth Include the Sharks, Chimeras, Rays, Skates, etc

Bony Fish

A bony fish’s skeleton is made with bones instead of cartilage. There are two main types of bony fish.

Ray-finned fish Lobe-finned fish
Eels, Mackerels, Sunfish, Tuna, and Atlantic cod are examples of this group

Fish Map of the World

Fish are present around the globe. There is no physical border in the oceans. However, different types are present in specific regions due to their physical abilities and food distribution.
facts about fish
Here is their main distribution of the world.

Fresh Water Fish

Freshwater fish are present in rivers, ponds, lakes, and streams around the globe. It includes catfish, carp, and various types of cichlids. Each part of the world has some specific types of freshwater fish. WWF said that about 51% of total fish species inhabit fresh water. These 18,000+ fish types make ¼ of all vertebrate species.

Marine Fish

These fish are present in oceans and seas. Their distribution depends on many factors, i.e., water currents, availability of food, and water temperature. There are 20,000+ species present in oceans. Some of them can equally live in marine and freshwater environments. Tuna, Mackerel, flounder, sharks, and rays are examples of marine fish.

Deep-See Fish

Many types of fish are present in the dark depths of water. These fish have characteristics that make them suitable to bear hydrostatic pressure, cold temperatures, and darkness. Mariana hadal snailfish is the deepest living fish at 27,460 feet below sea level. Angler fish, gulper eel, and Flashlight fish are examples of deep-sea fish.

Arctic and Antarctic Sea Fish

Arctic and antarctic fish live in icy conditions. Arctic fish include about 416 species, while the antarctic fish have 274 species. They include icefish, Arctic cod, and Antarctic toothfish.

Coral Reef Fish

Coral reefs host about 25% of all known marine species. Mostly, reef ecosystems are present in tropical and subtropical oceans. They host many colorful fish, i.e., butterfly fish, parrotfish, wrasse, etc.

Estuarine and Mangrove Fish

Several kinds of fish inhabit where the fresh and saline water meets. In 17 geographic regions, 740 fish species are reported in mangroves. About 75% of tropical fish are born in mangroves. Sheepshead, Grunts, Gobies, Schoolmasters, and Jacks are examples of such fish.

How Many Fish Are in the Ocean

It’s difficult to answer how many fish are in the ocean because they continually migrate and breed. Moreover, the number fluctuates due to many reasons. However, scientists said about 3 trillion+ fish and 20,000+ fish species are in the oceans. Scientists found about roughly 500 fish species each year.
Fun Facts About Fish

What Species of Fish Have Distinct Breeds

Close-related species cross with each other. It helps them with survival and color variation. Here are some such species.

Barb, Zebrafish, and Guppy These fish are naturally cross with different species. It helps them to optimize themselves with various survival techniques.
Clownfish Clownfish have two species, i.e., Amphiprion ocellaris and A. percula.
Goldfish Goldfish also have multiple breeds. Fantail, Comet, Moor, Lionhead, Oranda, and many others are examples of goldfish breeds that vary in color, finnage, and other physical traits.

Fun Facts About Fish

Here are some fun and mind-boggling facts about fish.

  • There are more fish than humans in the world.
  • The whale shark is the biggest fish at 50 feet in length. However, up to 20 meters is also reported.
  • The dwarf minnow is the smallest fish, i.e., less than 1 inch. The size varies among males and females.
  • The Bristle mouth fish are the most common in the world. They are present in deep water, i.e., 500 meters.
  • Methuselah, the Australian lungfish, is the oldest fish. It is about 90 to 100+ years old and can breathe air, unlike other fish.
  • Sucking mouth fish are the oldest animals in the world.
  • You can estimate any fish’s age by looking at the growth rings at the earbone.
  • Blue whales can live up to 80 to 90 years.
  • Fish breathe oxygen instead of air. Gills help to diffuse them in the bloodstream.
  • Fish don’t have eyelids. So, according to the dictionary, they don’t sleep. However, they rest by keeping them motionless or by decreasing the motion.
  • Fish can’t chew their food. Instead, they use their jaws or graze their food.
  • All fish are not edible. Some of them are prisoners, i.e., Pufferfish, Lionfish, etc.
  • Fish are odorless until they are alive. Also, they are not smelly if handled carefully.
  • Fish are the fastest swimmers. Sailfish, marlin, and tuna are their example.
  • Some fish can drown in water if there is insufficient oxygen.
  • Fish have small brains.
  • Not all fish lay eggs. Some give birth to the fish fry.
  • Seahorses can swim upright.


Thousands of fish species are distributed equally in freshwater, marine, deep sea, etc. Some fish evolve with time to survive in nature, and this causes different changes in them. Many fish species are also there. 3+ trillion with 20,000+ species is the exact answer to how many fish are in the ocean. This and many other facts about fish are part of this article. Let us know which fact you find interesting in the comment section. Moreover, to know more about fish and aquarium-related products, visit hygger official blog.

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