Fish: Different Types, Definitions, Photos, and More (original) (raw)

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 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

Cubera Snapper

There are three superclasses into which fish are grouped: Bony fish, jawless, and cartilaginous fish.

©Lynn Archer/Shutterstock.com

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.

For a list of incredible facts about fish, make sure to read ’10 Incredible Fish Facts.’

Diet

Fish eat crustaceans, plants, shrimp, and worms.

What do fish eat? Most species of fish fall into the omnivore category. This means that they can eat both plants and meat. It offers a wider range of food options for aquatic animals. It also helps fish find the different nutrition they need in a variety of foods.

Additionally, pet fish may have a bit of a different diet than fish you find in the wild. For example, pet fish mostly eat freeze-dried and frozen foods including bloodworms, brine shrimp, krill, and plankton.

Evolution and Origins

Oilfish

Oilfish contain high levels of wax esters, which are indigestible to humans.

©Porco_Rosso/Shutterstock.com

Fish have been evolving and changing for a very, very long time. Fish began to evolve during the Cambrian explosion approximately 530 million years ago. The earliest chordates formed skulls and spinal columns, which helped to evolve craniates and vertebrates. Additionally, the earliest fish lineages were the Agnatha or the jawless fish.

Early fish from fossil records are represented by a group of small armored and jawless fish. These were known as ostracoderm. These jawless fish lineages are mostly extinct now. However, an extant clade, the lampreys may have pre-dated the ancient pre-jawed fish. The first jaws were found in fossils and they lacked any teeth.

The diversity of these jawed creatures may prove the evolutionary advantages of a jawed mouth. Although interesting, it remains unclear if there was ever an advantage of a hinged jaw.

Furthermore, fish may have evolved from a creature similar to a coral sea squirt whose larva resembled primitive fish in very important ways.

Exceptions

Animals That Have Multiple Hearts: Hagfish

Hagfish are the only animals that have a skull but no vertebral column.

©Frank Fennema/Shutterstock.com

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.

You can read about some types of fish that are extinct.

Pregnancy

A Siamese female fighting fish guarding her newly laid eggs amongst the bubble nest.

©mnoor/Shutterstock.com

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 alive. 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.

Check out the fish gestation period.

Different Types of Fish:

Alligator Gar

The alligator gar has toxic eggs to protect against predators

American Eel

Don't eat raw eel! Their blood is poisonous to humans when consumed raw.

Anchovies

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

Anglerfish

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

Arapaima

One of the largest freshwater fish

Archerfish

Archerfish can shoot a stream of water up to five feet with amazing accuracy.

Arctic Char

Arctic char is the northern-most fish; no other fish lives anywhere further north!

Asian Carp

Asian carp can consume 40% of their body weight in food a day!

Atlantic Cod

One of the most popular food fishes in the world

Atlantic Salmon

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

Banjo Catfish

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

Barb

There are over 1768 known species!

Bass

Prized by sport fishers for their size and strength

Batfish

The batfish has a lure on its head to attract prey

Black Bass

The most popular game fish in North America

Blacknose Shark

When threatened, Blacknose sharks raise their head, arch their back, and lower their pectoral fins.

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 Shark

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

Blue Tang

One of the most colorful members of the genus Acanthurus

Bluefin Tuna

The bluefin is one of the largest fish in the world

Bluegill

The world record for longest bluegill is 15 inches.

Bonefish

Bonefish have migratory habits, moving from shallow waters to deeper waters during different times of the year.

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

Bronze Whaler Shark

Bronze whaler sharks often hunt in large groups, herding schools of fish into bait balls and going on a feeding frenzy.

Brook Trout

The Brook Trout is actually part of the salmon family, making it not technically a trout.

Buffalo Fish

The oldest Buffalo fish recorded was 112 years old!

Bull Trout

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

Carp

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

Catfish

There are nearly 3,000 different species!

Chinook Salmon

The Chinook salmon undertakes a long migration for the spawning season

Cichlid

There are more than 2 000 known species!

Cobia Fish

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

Codfish

Codfish are carnivorous and eat other fish, including young codfish.

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.

Cory Catfish

All Cory Catfish have three pairs of barbels around their mouth that they use to detect food.

Crappie Fish

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

Cubera Snapper

While very intimidating, the cubera snapper also falls prey to other marine animals like barracudas, whale sharks, and moray eels.

Damselfish

Damselfish belong to the family Pomacentridae

Danios

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

Discus

One of the only schooling Cichlids!

Dragon Eel

Dragon eels have double jaws and two sets of razor-sharp teeth

Dragonfish

Dragonfish can emit red light from their eyes

Drum Fish

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

Dusky Shark

The Dusky Shark sometimes eats trash discarded by humans.

Dwarf Gourami

Dwarf gourami can live for over four years with proper care.

Eel

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

Eel catfish

Eel catfish breathe air and reach up on land to catch beetles. Scientists think they may be a missing link between fish and lizards.

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.

Elephant Fish

Elephant fish are known as the Australian ghost shark, but they are not actually a shark species!

Ember Tetra

Ember tetras are one of the smallest shoaling fish in the world

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!

Fish

Respire through the gills on their heads!

Flathead Catfish

The only predators that prey on flathead catfish are members of their own species and humans who catch them for commercial and recreational purposes.

Florida Gar

The Florida gar has toxic eggs to protect against predators

Flounder

A flat fish found in the Atlantic and Pacific!

Flounder Fish

There are around 240 different species of Flounder fish

Flowerhorn Fish

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

Football Fish

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

Freshwater Drum

These fish are very vocal, and males make a rumbling or grunting noise during breeding season to attract a mate.

Freshwater Eel

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

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

Galapagos Shark

Galapagos sharks are cannibalistic and sometimes eat their young, so the pups stay away from the adults in shallow water.

Gar

Can grow to more than 3m long!

Garden Eel

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

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

Goonch Catfish

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

Gourami

Gourami fishes show parental care for their young

Grass Carp

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

Great Hammerhead Shark

Great hammerhead sharks have a 360-degree view because their eyes are situated on the ends of their mallet-like heads.

Green Sunfish

Juvenile Green Sunfish are less colorful than their parents because they need to blend in with their surroundings to avoid predators.

Grunion

Their whole bodies are edible

Gulper Eel

Gulper eels have a similar lifespan to humans and can live up to 85 years old. However, their age depends on their habitat and the availability of food.

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

Haikouichthys

Haikouichthys was the first animal to develop a well-defined head

Hairy Frogfish

Hairy frogfish can eat prey as large as themselves by swallowing them whole.

Halibut

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

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.

Horse Mackerel

Got their name from a myth that other fish would ride them over great distances

John Dory

The John Dory is often labeled one of the ugliest fish in the world and has no known relatives.

Kelp Greenling

Male Kelp Greenlings participate in an unusual mating ritual by fertilizing eggs in the nests of other males.

Keta Salmon

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

Keyhole Cichlid

When these fish feel stressed, their skin color will change from yellow-cream to brown.

Killifish

Killifish are highly sought after for their peaceful nature and ability to adapt to most aquarium communities.

Kissing Gourami

The kissing gesture that the kissing gourami displays is not a mating gesture

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!

Labout’s Fairy Wrasse

Females are sequential hermaphrodites, which means they can convert to males anytime during their life cycle.

Lake Trout

Darker specimens are sometimes called "mud hens"

Lancetfish

Lancetfish live at depths up to 6,500 feet below sea level

Largemouth Bass

Georgia, Mississippi, Alabama, and Florida all claim the largemouth bass as the state fish or state freshwater fish.

Leptocephalus

Leptocephali have flat bodies filled with jelly-like substances, surrounded by a thin layer of muscle.

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.

Mangrove Snapper

Tagging studies have found that once adults establish a habitat they typically remain there for long periods. In fact, they found that these fish can stay in one area for up to 4 years.

Masked Angelfish

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

Mayan Cichlid

Mayan cichlids live longer in captivity than they do in the wild.

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

Molly

Known for their calm and peaceful nature!

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!

Mullet Fish

The Striped Mullet is one of the best-known and most easily identified species, with black horizontal stripes along its body.

Muskellunge (Muskie)

In 1949, a Muskellunge set a world record by weighing 68 pounds and 8 ounces in Wisconsin.

Neon Tetra

Neon Tetras are very social and peaceful fish.

Oarfish

The Giant oarfish (Regalecus glesne) holds the Guinness Book of World Records for the longest bony fish in the world.

Ocean Perch

As a scorpionfish, the ocean perch has spines along its back!

Ocean Pout

Females guard their eggs for up to 3 months

Oilfish

They live in deep water as far as 2,600 feet below the water’s surface.

Opah

Opah are brightly colored, with red-orange fins and a silvery body.

Opaleye (Rudderfish)

Some indigenous people of the Pacific coast of North America consider opaleye fish sacred food and use it in traditional ceremonies.

Orchid Dottyback

This fish camouflages as its prey's parents to trick it into becoming dinner.

Oscar Fish

The Oscar fish has teeth in its throat!

Ozark Bass

Ozark Bass only live in Arkansas and Missouri

Pacific Sleeper Shark

In 2015, a Pacific Sleeper Shark was filmed living underneath an active volcano near the Solomon Islands. This shark is able to survive in waters with very high temperatures and acidity!

Paddlefish

Paddlefish have existed since the Cretaceous Period

Parrotfish

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

Peacock Bass

Peacock bass is known for their aggressive behavior and predatory instincts, making them a challenging target for sport fishermen.

Perch Fish

Some of the most delicious gamefish in the world

Pictus Catfish

Pictus catfish are social fish that should be kept in groups of 4 or more

Pinfish

Pinfish make loud croaking sounds during their spawning season.

Pipefish

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

Piranha

Generally found in fast-flowing streams!

Pollock Fish

Pollock is a nutritious fish, generally readily available for human consumption, and more sustainable and affordable than other whitefish species like hake or haddock.

Porbeagle Shark

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

Porcupinefish

The Porcupinefish secrete a potent neurotoxin known as tetrodotoxin; this poison can kill both people and predators.

Pufferfish

The second most poisonous creature in the world!

Pygmy Shark

Pygmy sharks underbelly glows to attract prey that swims beneath it.

Pyjama Shark

Pyjama Sharks like to swim in shallow inshore waters.

Rainbow Kribs (Kribensis)

Rainbow Kribs sometimes nip the fins of other fish, especially ones with long, flowing tails, which is too tempting for them not to bite.

Rainbow Shark

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

Red Drum Fish

There were a few sightings of red drums in the Mediterranean Sea off Sicily and Israel, but they do not naturally occur there, so theories are they escaped from fish farms.

Redhump Eartheater

The redhump eartheater are very passive fish and do well in aquariums with non-cichlid species

Reef Shark

Grey reef sharks can give birth without males

Rockfish

These fish can grow up to three feet long!

Sailfish

Fast billfish with a sail-like dorsal fin

Salmon

Returns upstream every year to spawn

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

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 Trout

Change colors in freshwater and saltwater

Seahorse

Males give birth to up to 1,000 offspring!

Shark

No shark species has any bones in their bodies

Sixgill shark

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

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.

Snailfish

The deepest ocean-dweller is a snailfish who was found over 26,700 feet below sea level.

Snook Fish

Males change into females after the spawning season

Snowflake Eel

Snowflake Eel have two jaws to help them swallow their food.

Sockeye Salmon

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

Spanish Mackerel

Spanish mackerel typically live to the age of 12, but there have been cases of these fish living as long as 25 years!

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.

Starfish

Has 2 stomachs to aid digestion!

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!

Striped Bass

Pilgrims counted striped bass as an essential part of their diet from the time they arrived in North America.

Sturgeon

Large species can swallow whole salmon

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

Swordfish

Lose their scales and teeth as adults

Taimen Fish

The Taimen is considered one of the oldest species on earth, with fossilized remains dating back more than 40 million years!

Tang

Found around shallow coral reefs!

Tarpon

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

Tetra

Native to the freshwater streams of South America!

Tiger Shark

The fourth biggest species of shark in the world!

Tiger Trout

As tiger trout are sterile, they cannot produce offspring. However, they do have relatively long lifespans and can live up to 10 years in captivity.

Triggerfish

There are 40 species of Triggerfish, all with different coloring and patterns.

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

Uaru Cichlid

The color of the Uaru cichlid changes during the spawning season

Viperfish

Viperfish have a bioluminescent spine on their dorsal fin.

Wahoo Fish

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

Wels Catfish

The Wels catfish is one the largest freshwater 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!

Xingu River Ray

The Xingu River ray is only found in the Xingu River in Brazil.

Xiphactinus

Xiphactinus was the largest bony fish of the Cretaceous Period.

Yellow Bass

Largest yellow bass ever recorded weighed 2.95 pounds

Zebra Pleco

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

List of Fish

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About the Author

Rebecca Bales

Rebecca is an experienced Professional Freelancer with nearly a decade of expertise in writing SEO Content, Digital Illustrations, and Graphic Design. When not engrossed in her creative endeavors, Rebecca dedicates her time to cycling and filming her nature adventures. When not focused on her passion for creating and crafting optimized materials, she harbors a deep fascination and love for cats, jumping spiders, and pet rats.

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.

What are the main differences between the flying fox fish and the Siamese algae eater?

The main differences between the flying fox fish and the Siamese algae eater are color, length and shape, mouth shape, and algae preferences.

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