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:

Alaskan Pollock

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

Albacore Tuna

The albacore is a very fast swimmer

Alligator Gar

The alligator gar has toxic eggs to protect against predators

Anchovies

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

Angelfish

There are 70 different species!

Anglerfish

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

Arapaima

One of the largest freshwater fish

Asian Arowana

The male Asian arowana raises the eggs in its mouth

Atlantic Salmon

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

Australian Flathead Perch

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

Baiji

Baijis use echolocation to find food in the Yangtze River.

Banana Eel

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

Banjo Catfish

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

Barb

There are over 1768 known species!

Barracuda

Can grow to nearly 2 meters long!

Barramundi Fish

Scale rings indicate age

Basking Shark

The second biggest fish in the world!

Batfish

The batfish has a lure on its head to attract prey

Beluga Sturgeon

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

Betta Fish (Siamese Fighting Fish)

Can live in low-oxygen environments!

Black Marlin

Every black marlin is born as a female.

Bladefin Basslet

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

Blobfish

One of the ugliest creatures in existence!

Blue Catfish

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

Blue Eyed Pleco

Can live safely with many types of fish.

Blue Shark

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

Bluefin Tuna

The bluefin is one of the largest fish in the world

Bluegill

The world record for longest bluegill is 15 inches.

Bonito Fish

May eat squid or other small invertebrate ocean life

Bonnethead Shark

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

Bowfin

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

Boxfish

Can release a toxin from its skin

Bull Trout

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

Butterfly Fish

There are more than 100 different species!

Carp

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

Catfish

There are nearly 3,000 different species!

Chimaera

Also called ghost shark

Chinese Paddlefish

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

Chinook Salmon

The Chinook salmon undertakes a long migration for the spawning season

Cichlid

There are more than 2 000 known species!

Clownfish

Also known as the anemonefish!

Cobia Fish

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

Codfish

They eat other fish

Coelacanth

The coelacanth first evolved almost 400 million years ago.

Conger Eel

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

Cookiecutter Shark

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

Crappie Fish

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

Danios

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

Discus

One of the only schooling Cichlids!

Dragonfish

Dragonfish can emit red light from their eyes

Drum Fish

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

Eel

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

Electric Catfish

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

Electric Eel

Despite its powerful shock, electric eels have terrible vision.

Escolar

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

Fangtooth

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

Fire Eel

Fire Eels are not true eels.

Fish

Respire through the gills on their heads!

Florida Gar

The Florida gar has toxic eggs to protect against predators

Flounder

A flat fish found in the Atlantic and Pacific!

Flowerhorn Fish

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

Fluke Fish (summer flounder)

The chameleon of the seas!

Flying Fish

Can glide in the air for hundreds of feet

Football Fish

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

Freshwater Eel

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

Freshwater Jellyfish

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

Frilled Shark

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

Frogfish

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

Gar

Can grow to more than 3m long!

Garden Eel

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

Ghost Catfish

You can see its heart beating

Goblin Shark

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

Goldfish

Goldfish and common carp can mate and produce offspring

Goliath Tigerfish

Featured in River Monsters TV series

Goonch Catfish

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

Grass Carp

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

Great White Shark

Can grow to more than 8 meters long!

Greenland Shark

This shark has the longest lifespan of any vertebrate.

Grey Reef Shark

One of the most common shark species!

Guppy

Also known as the Millionfish!

Haddock

The haddock is very popular in both recreational and commercial fishing

Hagfish

Can use slime to suffocate marine predators or escape capture

Halibut

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

Hammerhead Shark

Found in coastal waters around the world!

Hardhead Catfish

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

Herring

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

Horn Shark

Endemic to the Californian coast!

Immortal Jellyfish

Excellent hitchhiker on long-trip cargo ships

Jellyfish

Have tentacles around their mouths!

Keta Salmon

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

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.

Krill

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

Lake Sturgeon

Its skeleton is part cartilage and part bone.

Lamprey

Not related to the eel

Lawnmower Blenny

Must be in temperatures of 78 degrees Fahrenheit to breed

Lionfish

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

Lizardfish

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

Loach

Have sharp spines below their eyes

Longnose Gar

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

Lumpfish

The lumpfish have sticky suction cups on their fins

Lungfish

The lungfish first evolved almost 400 million years ago.

Mahi Mahi (Dolphin Fish)

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

Manta Ray

Can grow up to 9m wide!

Masked Angelfish

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

Megalodon

The largest shark to ever live!

Megamouth Shark

Swims with its mouth open to capture prey

Mekong Giant Catfish

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

Milkfish

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

Mojarra

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

Mola mola (Ocean Sunfish)

The ocean sunfish is the biggest bony fish in the world

Molly

Known for their calm and peaceful nature!

Monkfish

Called "The Poor Man's Lobster!"

Moon Jellyfish

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

Moray Eel

Sometimes, groupers invite moray eels to help them hunt!

Needlefish

no stomach to digest food

Neptune Grouper

The largest recorded specimen ever caught was 17" long

Nurse Shark

Commonly found in Central American waters!

Oscar Fish

The Oscar fish has teeth in its throat!

Oyster Toadfish

The oyster toadfish can produce poison to protect itself

Paddlefish

Paddlefish have existed since the Cretaceous Period

Parrotfish

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

Peppermint Angelfish

The peppermint angelfish was only first described in 1992.

Pike Fish

Apex freshwater predators with fearsome teeth!

Pipefish

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

Piranha

Generally found in fast-flowing streams!

Platinum Arowana

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

Porbeagle Shark

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

Pufferfish

The second most poisonous creature in the world!

Rainbow Shark

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

Red-Lipped Batfish

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

Redtail Catfish

One of three giant catfish species

Reef Shark

Grey reef sharks can give birth without males

Rockfish

These fish can grow up to three feet long!

Salmon

Returns upstream every year to spawn

Salmon Shark

Salmon sharks are related to Great Whites.

Sand Tiger Shark

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

Sardines

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

Sawfish

Sawfish teeth keep growing as the fish gets older

Scorpion Fish

There are more than 200 recognised species!

Sculpin

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

Sea Dragon

Inhabits tropical coastal waters of Australia!

Sea Slug

All sea slugs have both male and female sex organs

Sea Urchin

Can live for up to 200 years!

Seahorse

Males give birth to up to 1,000 offspring!

Shark

No shark species has any bones in their bodies

Silver Dollar

Closely related to the Piranha

Sixgill shark

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

Skate Fish

More than 200 species exist!

Skipjack Tuna

The skipjack is the most commonly caught tuna in the world

Sleeper Shark

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

Snook Fish

Males change into females after the spawning season

Sockeye Salmon

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

Spinner Shark

Can have up to 20 babies

Spiny Dogfish

Found in ocean waters worldwide!

Sponge

There are more than 9,000 known species!

Spotted Gar

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

Squirrelfish

Uses vibrations to communicate with other fish

Starfish

Has 2 stomachs to aid digestion!

Stargazer Fish

Uses an electric shock to stun its prey!

Steelhead Salmon

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

Stingray

It's stinger is razor-sharp or serrated!

Sturgeon

Large species can swallow whole salmon

Sucker Fish

Commonly found throughout America!

Surgeonfish

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

Swai Fish

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

Tang

Found around shallow coral reefs!

Tarpon

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

Telescope Fish

Swallows food, much of it larger than them, whole

Tetra

Native to the freshwater streams of South America!

Tiger Shark

The fourth biggest species of shark in the world!

Tire Track Eel

They like to burrow into aquarium sand.

Toadfish

Can be heard out of water

Trout

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

Tuna

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

Viper shark (dogfish)

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

Wahoo Fish

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

Walking Catfish

The walking catfish can move on land while breathing air

Walleye Fish

Has great night vision

Wels Catfish

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

Whale Shark

The largest species of fish in the world!

Whiting

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

Wolf Eel

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

Wolffish

The wolffish has impressive canines with a powerful bite force!

Wrasse

There are more than 500 different species!

Wrought Iron Butterflyfish

Is endemic to Japan.

Yellowfin Tuna

The yellowfin forms schools with other tuna species

Zebra Pleco

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

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.