Fish: Different Types, Definition, Photos, and More

Fish are aquatic vertebrates. They usually have gills, paired fins, a long body covered with scales, and tend to be cold-blooded. “Fish” is a term used to refer to lampreys, sharks, coelacanths, and ray-finned fishes, but is not a taxonomic group, which is a clade or group containing a common ancestor and all its descendants. Instead, there are 3 main classes, groups, or types of fish: bony fish (Osteichthyes), jawless fish (Agnatha), and cartilaginous fish (Chondrichthyes). Fish are the most diverse group among the vertebrates, with over 33,000 different types of fish species.

No one really knows how many different types of fish exist in the world, more are being discovered constantly. We may soon have over 35,000, or even 40,000 known species!

5 Fish Characteristics

There are three superclasses into which fish are grouped: Bony fish (Osteichthyes), jawless fish (Agnatha), and cartilaginous fish (Chondrichthyes). Ray-finned fishes are of the class Actinopterygii, while lobe-finned fishes are of the class Sarcopterygii. Both are clades of bony fishes.

Regardless, all fish have some characteristics in common that distinguish them from other animals.

  • Cold-bloodedness: All fish are ectothermic or cold-blooded, meaning they cannot regulate their internal body temperature. Even warm-blooded fish such as tuna and mackerel sharks have only “regional endothermy” or warm-bloodedness limited to certain areas.
  • Water habitat: All fish live in bodies of water, whether it is freshwater or saltwater. However, not all creatures that live in water are fish.
  • Gills to breathe: Fish have gills throughout their life cycle. As with the water habitat, although all fish have gills, not all creatures with gills are fish.
  • Swim bladders: Specialized organs fill with air to keep the fish afloat and in some species help them survive with low oxygen levels. They also help fish sleep and are sensitive enough to detect the movement of food and predators.
  • Fins for movement: Most common are a tail fin, a pair of side fins, a dorsal fin and an anal fin. Variations exist but they all provide motion, maneuverability and stability.

Fish Exceptions

There are several exceptions to the common definition of a fish. For example, hagfish don’t have scales and aren’t true vertebrates (or are considered primitive vertebrates); mudskippers are amphibious fish that can live outside water; lungfish use lungs instead of gills to breathe; lampreys lack paired fins, and tuna are warm-blooded.

Also, not all fish groups come from fish lineages. The superclass Tetrapoda of the four-listed animals is considered to be a group within Sarcopterygii, and includes amphibians, reptiles, birds, and mammals. Hence, Sarcopterygii includes both lobe-finned fishes and tetrapods.

Finally, not all aquatic creatures which resemble fish are considered fish. Whales, dolphins, and porpoises are aquatic mammals, for example.

Fish Pregnancy

  • There are two main types of fish pregnancies, ovoviviparity or aplacental viviparity (egg-bearing) and viviparous (embryo-bearing). Both are considered to be live-bearing.
  • Ovoviparity has the eggs develop and hatch internally, with the young being born live. It can express either ovuliparity (external fertilization of eggs and zygote development), oviparity (internal fertilization of eggs and external development of zygotes as eggs with yolks), or ovoviviparity (internal fertilization of eggs and internal development of embryos with yolks). Stingrays, seahorses and some shark species are ovoviviparous. So are guppies, mollies, swordtails, halfbeaks and platies.
  • Viviparity has embryos develop internally before being born live. It can express either histotrophic (“tissue-eating”) viviparity (mother provides no nutrition and embryos eat their unborn siblings or mother’s unfertilized eggs) or hemotrophic (“blood-eating) viviparity (mother provides nutrition, usually through a placenta). Many shark species are viviparous.

Different Types of Fish:

A Alaskan Pollock
Alaskan Pollock

It's one of the most commonly eaten fish in the world

A Albacore Tuna
Albacore Tuna

The albacore is a very fast swimmer

A Alligator Gar
Alligator Gar

The alligator gar has toxic eggs to protect against predators

A Anchovies
Anchovies

November 12th is celebrated as National Pizza with the Works Except Anchovies Day

A Angelfish
Angelfish

There are 70 different species!

A Anglerfish
Anglerfish

The anglerfish has a glowing lure on its head to attract unsuspecting prey

A Arapaima
Arapaima

One of the largest freshwater fish

A Asian Arowana
Asian Arowana

The male Asian arowana raises the eggs in its mouth

A Atlantic Salmon
Atlantic Salmon

These fish are known for their ability to leap and fight when hooked.

A Australian Flathead Perch
Australian Flathead Perch

This small fish fetches a high price tag, with individuals selling from $1,000 to $5,000.

A Baiji
Baiji

Baijis use echolocation to find food in the Yangtze River.

A Banana Eel
Banana Eel

Named for the yellow body and brown spots that make it look like a banana.

A Banjo Catfish
Banjo Catfish

The banjo catfish is extremely shy and known for hiding from onlookers.

A Barb
Barb

There are over 1768 known species!

A Barracuda
Barracuda

Can grow to nearly 2 meters long!

A Barramundi Fish
Barramundi Fish

Scale rings indicate age

A Batfish
Batfish

The batfish has a lure on its head to attract prey

A Beluga Sturgeon
Beluga Sturgeon

The beluga sturgeon is one of the largest bony fish in the world!

A Betta Fish (Siamese Fighting Fish)
Betta Fish (Siamese Fighting Fish)

Can live in low-oxygen environments!

A Black Marlin
Black Marlin

Every black marlin is born as a female.

A Bladefin Basslet
Bladefin Basslet

The tiny bladefin basslet belongs to the same subfamily as the giant grouper, Epinephelinae.

A Blobfish
Blobfish

One of the ugliest creatures in existence!

A Blue Catfish
Blue Catfish

It's a strong fighter when caught on a fishing line

A Blue Eyed Pleco
Blue Eyed Pleco

Can live safely with many types of fish.

A Blue Shark
Blue Shark

Blue sharks can have up to 135 pups at a time.

A Bluefin Tuna
Bluefin Tuna

The bluefin is one of the largest fish in the world

A Bluegill
Bluegill

The world record for longest bluegill is 15 inches.

A Bonito Fish
Bonito Fish

May eat squid or other small invertebrate ocean life

A Bonnethead Shark
Bonnethead Shark

Bonnetheads are the only hammerhead sharks that use their pectoral fins to swim.

A Bowfin
Bowfin

The bowfin is a primitive fish that first evolved in the Jurassic

A Boxfish
Boxfish

Can release a toxin from its skin

A Bull Trout
Bull Trout

The bull trout is not actually a trout, but a member of the char family.

A Butterfly Fish
Butterfly Fish

There are more than 100 different species!

A Carp
Carp

The carp is one of the most popular pond fishes in the world

A Catfish
Catfish

There are nearly 3,000 different species!

A Chimaera
Chimaera

Also called ghost shark

A Chinese Paddlefish
Chinese Paddlefish

The Chinese paddlefish is one the largest freshwater fish in the world

A Chinook Salmon
Chinook Salmon

The Chinook salmon undertakes a long migration for the spawning season

A Cichlid
Cichlid

There are more than 2 000 known species!

A Clownfish
Clownfish

Also known as the anemonefish!

A Cobia Fish
Cobia Fish

It has teeth not only in its jaws but in its tongue and the roof of its mouth

A Codfish
Codfish

They eat other fish

A Coelacanth
Coelacanth

The coelacanth first evolved almost 400 million years ago.

A Conger Eel
Conger Eel

The European Conger ( Conger conger) can weigh as much as an adult human!

A Cookiecutter Shark
Cookiecutter Shark

The cookiecutter shark takes its name because it leaves a cookie-shaped bite hole in its prey.

A Crappie Fish
Crappie Fish

The crappie is one of the most popular freshwater fish in North America.

A Danios
Danios

These fish make a popular choice for aquarium hobbyists due to their hardy nature.

A Discus
Discus

One of the only schooling Cichlids!

A Dragonfish
Dragonfish

Dragonfish can emit red light from their eyes

A Drum Fish
Drum Fish

The drum fish makes a croaking sound with its swimming bladder!

A Eel
Eel

Eels can be a mere few inches long to 13 feet!

A Electric Catfish
Electric Catfish

The electric catfish can discharge an electric shock up to 450 volts

A Electric Eel
Electric Eel

Despite its powerful shock, electric eels have terrible vision.

A Escolar
Escolar

Its system can’t metabolize wax esters, which can lead to unpleasantness for diners.

A Fangtooth
Fangtooth

Has the largest teeth compared to body size of any known fish

A Fire Eel
Fire Eel

Fire Eels are not true eels.

A Fish
Fish

Respire through the gills on their heads!

A Florida Gar
Florida Gar

The Florida gar has toxic eggs to protect against predators

A Flounder
Flounder

A flat fish found in the Atlantic and Pacific!

A Flowerhorn Fish
Flowerhorn Fish

The Flowerhorn fish is an artificial species; it does not exist naturally

A Fluke Fish (summer flounder)
Fluke Fish (summer flounder)

The chameleon of the seas!

A Flying Fish
Flying Fish

Can glide in the air for hundreds of feet

A Football Fish
Football Fish

The football fish is named after its unusual round or oblong shape

A Freshwater Eel
Freshwater Eel

Freshwater eels are actually catadromous, meaning they migrate to saltwater to spawn

A Freshwater Jellyfish
Freshwater Jellyfish

The freshwater jellyfish is native to China but is now found all over the world

A Frilled Shark
Frilled Shark

Frilled Sharks got their name from the six rows of gills on their throat that look like ruffled collars.

A Frogfish
Frogfish

The frogfish can change colors, but it takes several weeks to do so

A Gar
Gar

Can grow to more than 3m long!

A Garden Eel
Garden Eel

Garden eel colonies are made up of hundreds to thousands of individuals.

A Ghost Catfish
Ghost Catfish

You can see its heart beating

A Goblin Shark
Goblin Shark

Goblin Sharks are called a living fossil because their family, Mitsukurinidae, can be traced back 125 million years.

A Goldfish
Goldfish

Goldfish and common carp can mate and produce offspring

A Goliath Tigerfish
Goliath Tigerfish

Featured in River Monsters TV series

A Goonch Catfish
Goonch Catfish

The goonch catfish, or giant devil catfish, is one of the most fierce freshwater fish.

A Grass Carp
Grass Carp

The grass carp is considered to be a natural weed control agent.

A Great White Shark
Great White Shark

Can grow to more than 8 meters long!

A Greenland Shark
Greenland Shark

This shark has the longest lifespan of any vertebrate.

A Grey Reef Shark
Grey Reef Shark

One of the most common shark species!

A Guppy
Guppy

Also known as the Millionfish!

A Haddock
Haddock

The haddock is very popular in both recreational and commercial fishing

A Hagfish
Hagfish

Can use slime to suffocate marine predators or escape capture

A Halibut
Halibut

The word "halibut" is comes from haly meaning "holy" and butte meaning flat fish due to its popularity on Catholic holy days.

A Hammerhead Shark
Hammerhead Shark

Found in coastal waters around the world!

A Hardhead Catfish
Hardhead Catfish

The hardhead catfish has a sharp spine near its fin to inject venom

A Herring
Herring

People enjoy the taste of the oily fish in many different ways including pickled, smoked, salted, dried and fermented.

A Horn Shark
Horn Shark

Endemic to the Californian coast!

A Immortal Jellyfish
Immortal Jellyfish

Excellent hitchhiker on long-trip cargo ships

A Jellyfish
Jellyfish

Have tentacles around their mouths!

A Keta Salmon
Keta Salmon

During spawning the look of the male changes. Among other things, he grows a beak called a kype that bears fangs.

A Koi Fish
Koi Fish

In Japanese, the word koi sounds like the word for love. So the fish is a symbol of love among other good things.

A Krill
Krill

The krill is perhaps the most important animal in the marine ecosystem!

A Lake Sturgeon
Lake Sturgeon

Its skeleton is part cartilage and part bone.

A Lamprey
Lamprey

Not related to the eel

A Lawnmower Blenny
Lawnmower Blenny

Must be in temperatures of 78 degrees Fahrenheit to breed

A Lionfish
Lionfish

Females can release up to 15,000 eggs at a time!

A Lizardfish
Lizardfish

The lizardfish can camouflage itself against the sandy bottom to avoid predators.

A Loach
Loach

Have sharp spines below their eyes

A Longnose Gar
Longnose Gar

The longnose gar species of the gar family has potentially existed for 100 million years.

A Lumpfish
Lumpfish

The lumpfish have sticky suction cups on their fins

A Lungfish
Lungfish

The lungfish first evolved almost 400 million years ago.

A Mahi Mahi (Dolphin Fish)
Mahi Mahi (Dolphin Fish)

It's called the rabbit of the ocean because it multiplies so quickly.

A Manta Ray
Manta Ray

Can grow up to 9m wide!

A Masked Angelfish
Masked Angelfish

All masked angelfish are female until sometime after sexual maturity, at which point some become male.

A Megalodon
Megalodon

The largest shark to ever live!

A Megamouth Shark
Megamouth Shark

Swims with its mouth open to capture prey

A Mekong Giant Catfish
Mekong Giant Catfish

The Mekong giant catfish is the largest purely freshwater fish in the world

A Milkfish
Milkfish

Females lay up to 5 million eggs at one time in warm, shallow and salty waters

A Mojarra
Mojarra

The mojarra's protruding mouth allows it to sift along the seabed for food

A Mola mola (Ocean Sunfish)
Mola mola (Ocean Sunfish)

The ocean sunfish is the biggest bony fish in the world

A Molly
Molly

Known for their calm and peaceful nature!

A Monkfish
Monkfish

Called "The Poor Man's Lobster!"

A Moon Jellyfish
Moon Jellyfish

Moon Jellies are bioluminescent, so they glow in the dark! They can also de-age!

A Moray Eel
Moray Eel

Sometimes, groupers invite moray eels to help them hunt!

A Needlefish
Needlefish

no stomach to digest food

A Neptune Grouper
Neptune Grouper

The largest recorded specimen ever caught was 17" long

A Nurse Shark
Nurse Shark

Commonly found in Central American waters!

A Oscar Fish
Oscar Fish

The Oscar fish has teeth in its throat!

A Oyster Toadfish
Oyster Toadfish

The oyster toadfish can produce poison to protect itself

A Paddlefish
Paddlefish

Paddlefish have existed since the Cretaceous Period

A Parrotfish
Parrotfish

The parrotfish can change from female to male at some point in its life.

A Peppermint Angelfish
Peppermint Angelfish

The peppermint angelfish was only first described in 1992.

A Pike Fish
Pike Fish

Apex freshwater predators with fearsome teeth!

A Pipefish
Pipefish

The male pipefish has the ability to carry fertilized eggs with him

A Piranha
Piranha

Generally found in fast-flowing streams!

A Platinum Arowana
Platinum Arowana

The male broods the eggs and baby fish in his mouth.

A Porbeagle Shark
Porbeagle Shark

The porbeagle is one of the few sharks that jumps out of the water

A Pufferfish
Pufferfish

The second most poisonous creature in the world!

A Rainbow Shark
Rainbow Shark

The rainbow shark has been genetically modified to glow in the dark

A Red-Lipped Batfish
Red-Lipped Batfish

Despite its weird looks, the red-lipped batfish is harmless to humans

A Redtail Catfish
Redtail Catfish

One of three giant catfish species

A Reef Shark
Reef Shark

Grey reef sharks can give birth without males

A Rockfish
Rockfish

These fish can grow up to three feet long!

A Salmon
Salmon

Returns upstream every year to spawn

A Salmon Shark
Salmon Shark

Salmon sharks are related to Great Whites.

A Sand Tiger Shark
Sand Tiger Shark

The sand tiger is the shark most commonly seen in aquariums.

A Sardines
Sardines

Schools of sardines can be miles long and are often visible from an airplane

A Sawfish
Sawfish

Sawfish teeth keep growing as the fish gets older

A Scorpion Fish
Scorpion Fish

There are more than 200 recognised species!

A Sculpin
Sculpin

Its skull bones can compress so the fish can fit in narrow spaces

A Sea Dragon
Sea Dragon

Inhabits tropical coastal waters of Australia!

A Sea Slug
Sea Slug

All sea slugs have both male and female sex organs

A Sea Urchin
Sea Urchin

Can live for up to 200 years!

A Seahorse
Seahorse

Males give birth to up to 1,000 offspring!

A Shark
Shark

No shark species has any bones in their bodies

A Silver Dollar
Silver Dollar

Closely related to the Piranha

A Sixgill shark
Sixgill shark

The sixgill shark has six pairs of gills instead of the normal five

A Skate Fish
Skate Fish

More than 200 species exist!

A Skipjack Tuna
Skipjack Tuna

The skipjack is the most commonly caught tuna in the world

A Sleeper Shark
Sleeper Shark

The Greenland shark is one of the longest living vertebrates in the world.

A Snook Fish
Snook Fish

Males change into females after the spawning season

A Sockeye Salmon
Sockeye Salmon

Called "red salmon" because their skin turns bright red to dirty red during spawning season

A Spinner Shark
Spinner Shark

Can have up to 20 babies

A Spiny Dogfish
Spiny Dogfish

Found in ocean waters worldwide!

A Sponge
Sponge

There are more than 9,000 known species!

A Spotted Gar
Spotted Gar

They are commonly mistaken as logs in the water due to their cylindrical body.

A Squirrelfish
Squirrelfish

Uses vibrations to communicate with other fish

A Starfish
Starfish

Has 2 stomachs to aid digestion!

A Stargazer Fish
Stargazer Fish

Uses an electric shock to stun its prey!

A Steelhead Salmon
Steelhead Salmon

Steelhead live in freshwater rivers and streams for 1 to 2 years before migrating into the ocean

A Stingray
Stingray

It's stinger is razor-sharp or serrated!

A Sturgeon
Sturgeon

Large species can swallow whole salmon

A Sucker Fish
Sucker Fish

Commonly found throughout America!

A Surgeonfish
Surgeonfish

Paracanthurus hepatus, the palette surgeonfish or bluetang, is the only member of its genus

A Swai Fish
Swai Fish

The edges of an iridescent shark's fins have a signature glow

A Tang
Tang

Found around shallow coral reefs!

A Tarpon
Tarpon

Its genus dates back to the Cretaceous period – 113 million years ago

A Telescope Fish
Telescope Fish

Swallows food, much of it larger than them, whole

A Tetra
Tetra

Native to the freshwater streams of South America!

A Tire Track Eel
Tire Track Eel

They like to burrow into aquarium sand.

A Toadfish
Toadfish

Can be heard out of water

A Trout
Trout

They don’t have scales for their first month of life!

A Tuna
Tuna

The tuna has a sleek body that enables it to swim quickly through the water

A Viper shark (dogfish)
Viper shark (dogfish)

Most data on these fish is based on observations near Japan.

A Wahoo Fish
Wahoo Fish

Wahoo can change colors when they're excited and while they hunt

A Walking Catfish
Walking Catfish

The walking catfish can move on land while breathing air

A Walleye Fish
Walleye Fish

Has great night vision

A Wels Catfish
Wels Catfish

The wels catfish is among the largest freshwater fish in the world.

A Whale Shark
Whale Shark

The largest species of fish in the world!

A Whiting
Whiting

"Whiting" can refer to certain other species of ray-finned fish

A Wolf Eel
Wolf Eel

Wolf Eels may become tame and interact with human in areas where people frequently dive.

A Wolffish
Wolffish

The wolffish has impressive canines with a powerful bite force!

A Wrasse
Wrasse

There are more than 500 different species!

A Wrought Iron Butterflyfish
Wrought Iron Butterflyfish

Is endemic to Japan.

A Yellowfin Tuna
Yellowfin Tuna

The yellowfin forms schools with other tuna species

A Zebra Pleco
Zebra Pleco

The zebra pleco is a bottom feeder with a sucker mouth.

A Zebra Shark
Zebra Shark

Can get to be 30 years old in the wild!

List of Fish

Fish: Different Types, Definition, Photos, and More FAQs (Frequently Asked Questions) 

What are the 3 types of fish?

Bony fish, jawless fish and cartilaginous fish.

What's the most famous fish?

The most famous fish is the coelacanth, which has four lobed fins resembling limbs. It is one of the world’s most ancient fish species. Its name means “hollow spine” and comes from the Greek words koilos (hollow) and akantha (spine).
Coelacanth also refers to the order Coelacanthiformes. which comes from the clade Sarcopterygii and subclass Actinistia. It includes two species in the genus Latimeria: the West Indian Ocean coelacanth (Latimeria chalumnae) and the Indonesian coelacanth (Latimeria menadoensis).

Can fish feel pain?

Yes, fish can feel pain, but it is different from the expression of pain from humans. It is difficult to test fish for pain except by looking for unusual behavior and physiological responses in reaction to certain stimuli.

What do fish eat?

Fish can be predatory, foraging or filter-feeding. Their diets can be carnivorous or omnivorous depending on the species and can include prey from zooplankton to invertebrates, crustaceans, annelids and smaller fish.

Discover a fish with human-like teeth here!

How do fish breathe?

Fish usually breathe through gills, which filters oxygen through water. However, some fish breathe using different means. Lungfish have lungs and mudskippers can breathe through wet skin and the lining of their mouth and throat.

What are the smallest and largest fish?

The smallest fish is the cyprinid fish (8mm) and the largest fish is the whale shark (12m).

What is the difference between "fish" and "fishes"?

“Fish” refers to the singular and one species or to the plural within context. “Fishes” refers to the plural, especially when talking about more than one species of fish.