Fish Facts & Images, What is a Fish?

What is a Fish

Table of Contents

Fish Facts

Feature	Details
Common Name	Fish (collective term for a superclass of aquatic vertebrates)
Scientific Classification	Multiple classes: Actinopterygii, Chondrichthyes, Sarcopterygii, Agnatha
Kingdom	Animalia
Phylum	Chordata
Estimated Species	~36,000+ known species (2026)
Lifespan Range	Days (pygmy goby) to 500+ years (Greenland shark)
Weight Range	<1 gram (dwarf minnow) to 21,500 kg (whale shark)
Size Range	8 mm (Paedocypris progenetica) to 12+ m (whale shark)
Diet	Omnivores, carnivores, herbivores, filter feeders, detritivores
Habitat	Every aquatic environment on Earth
Global Biomass	~0.8 billion tonnes (estimated)
Conservation Status	Varies — many species Critically Endangered
Oldest Fossil Evidence	~530 million years ago (Cambrian period)
% of All Vertebrates	Fish make up approximately 50% of all vertebrate species

1. Fish Species Overview & Scientific Classification

Dive beneath the surface of any body of water on Earth — a tropical coral reef, a frigid Arctic lake, a pitch-black deep-ocean trench, even an underground cave system — and you will almost certainly find fish. They are everywhere. They are ancient. They are astonishingly diverse. And they are, without question, the most successful group of vertebrates that has ever lived on this planet.

“Fish” is not, strictly speaking, a single biological group. It is a convenient collective term for an enormous and wildly varied assemblage of aquatic, gill-breathing, typically cold-blooded vertebrate animals. To say “fish” encompasses everything from the 8 mm Paedocypris progenetica — the world’s smallest vertebrate, barely larger than a mosquito — to the 12-metre whale shark, the largest fish and largest non-mammalian vertebrate on Earth. It includes the electric eel that generates 800-volt shocks, the anglerfish that lures prey with a bioluminescent lantern in the abyss, the lungfish that breathes air and can survive years without water, and the humble goldfish sitting in a glass bowl on your windowsill.

With over 36,000 known species as of 2026 — and scientists estimating that hundreds more remain undiscovered — fish represent approximately half of all vertebrate species on Earth. They have colonized every aquatic environment our planet offers, from the sunlit surface waters of tropical oceans to hydrothermal vent systems 4,000 metres below the sea surface, where temperatures near boiling and pressure would crush a human body in seconds.

Species Classification Table

Group	Class	Example Species	# Known Species
Ray-finned Fish	Actinopterygii	Salmon, tuna, goldfish, clownfish	~30,000+
Cartilaginous Fish	Chondrichthyes	Sharks, rays, skates, chimaeras	~1,100+
Lobe-finned Fish	Sarcopterygii	Coelacanth, lungfishes	~8 living species
Jawless Fish	Agnatha (Cyclostomata)	Lampreys, hagfish	~120+

Ray-finned fish — the Actinopterygii — are by far the dominant group, comprising roughly 96% of all fish species. Their fins are webs of skin supported by bony rays, giving them extraordinary maneuverability. This group includes virtually every fish most people would recognize: salmon, trout, cod, bass, tuna, goldfish, guppies, clownfish, and thousands more.

“In every outthrust headland, in every curving beach, in every grain of sand, there is the story of the earth.” — Rachel Carson, marine biologist and author of The Sea Around Us, on the ocean and its inhabitants

2. Fish Physical Description & Unique Features

If there is one word that defines fish as a group, it is diversity. No other class of vertebrates displays such extraordinary variation in body shape, color, size, physiology, and adaptation. Yet beneath that diversity, certain fundamental features unite the group.

The Basic Fish Body Plan

Most fish share a streamlined, laterally compressed body optimized for movement through water. This fusiform shape minimizes drag — a principle so effective that human engineers have copied it in everything from submarines to aircraft. Key anatomical features common to most fish include:

Gills — the defining respiratory organ of fish, extracting dissolved oxygen directly from water as it passes over delicate, blood-rich filaments
Fins — used for propulsion, steering, and stability; the specific number and arrangement varies dramatically across species
Scales — protective outer covering; vary from the heavy, bony scales of carp to the microscopic, tooth-like dermal denticles of sharks
Lateral line — a sensory organ running along the length of the body that detects pressure changes and vibrations in the water, effectively giving fish a “sixth sense” for movement around them
Swim bladder — a gas-filled organ present in most ray-finned fish that provides buoyancy, allowing fish to hover effortlessly at a chosen depth

Extraordinary Physical Adaptations

The Anglerfish: Deep-sea anglerfish females carry a bioluminescent lure — the esca — on a modified dorsal spine above their mouths. In the pitch darkness of the deep ocean, this living light dangles and pulses to attract prey, sometimes larger than the fish itself.

The Archerfish: This remarkable freshwater fish from Southeast Asia can spit jets of water up to 3 metres into the air with extraordinary accuracy, knocking insects off overhanging vegetation — compensating for light refraction between water and air to aim precisely.

The Mimic Octopus is famous for its mimicry, but the mimic filefish (Paraluterus prionurus) takes a simpler approach — it has evolved to look almost identical to the toxic pufferfish, gaining protection through resemblance.

The Greenland Shark (Somniosus microcephalus) grows so slowly it may not reach sexual maturity until it is 150 years old, and individuals have been dated at over 500 years of age — making them the longest-lived vertebrates on Earth.

Did You Know? The coelacanth (Latimeria chalumnae) — a lobe-finned fish — was believed to have gone extinct 66 million years ago along with the dinosaurs. Then, in 1938, a living specimen was caught off the coast of South Africa, making it one of the most astonishing zoological discoveries in history. Living coelacanths have changed so little in 400 million years that scientists call them a “living fossil.”

3. Natural Habitat & Geographic Range

Fish inhabit virtually every aquatic environment on Earth with almost no exceptions. Their ecological reach is staggering — from the sunlit, warm shallows of tropical coral reefs to permanently frozen Arctic lakes, from swift Himalayan mountain torrents to the crushing darkness of the Mariana Trench (nearly 11,000 metres below sea level).

Habitat Range by Environment

Habitat Type	Examples	Notable Species
Tropical Coral Reefs	Great Barrier Reef, Caribbean	Clownfish, parrotfish, reef sharks
Open Ocean (Pelagic)	Pacific, Atlantic, Indian Ocean	Tuna, marlin, whale shark, mahi-mahi
Deep Sea (Abyssal)	Midnight zone, 1,000–11,000 m	Anglerfish, viperfish, giant oarfish
Freshwater Rivers	Amazon, Nile, Mekong	Piranha, arapaima, river dolphin fish
Freshwater Lakes	Lake Baikal, Lake Tanganyika	Cichlids, Baikal oilfish, sturgeon
Polar Oceans	Arctic, Antarctic	Icefish, Greenland shark, Arctic char
Estuaries/Mangroves	Coastal wetlands worldwide	Mudskipper, snook, juvenile reef fish
Caves (Hypogean)	Underground aquifers	Mexican tetra (blind cavefish)
Hydrothermal Vents	Mid-ocean ridge systems	Vent eelpout, snailfish

Habitat Range by Continent

Continent/Region	Freshwater Species	Marine Species	Notable Fact
South America	6,000+	1,500+	Amazon basin has world’s richest freshwater fish diversity
Africa	3,400+	2,000+	Lake Tanganyika alone has 350+ unique cichlid species
Asia	3,000+	3,000+	Mekong River system: 1,000+ freshwater species
North America	1,000+	2,000+	Great Lakes host 180+ native species
Europe	546+	1,000+	Danube River has 100+ species
Australia/Oceania	300+	4,000+	Great Barrier Reef hosts 1,500+ fish species
Polar Regions	Limited	300+	Antarctic icefish have antifreeze proteins in blood

Did You Know? The snailfish (Pseudoliparis swirei), discovered in the Mariana Trench, holds the record as the deepest fish ever recorded — observed at a depth of 8,336 metres in 2023. At this depth, the pressure is equivalent to 800 atmospheres — like having 50 jumbo jets stacked on top of you.

4. Diet & Feeding Behavior

Fish have evolved into virtually every dietary niche that aquatic ecosystems offer. Their feeding strategies are as diverse as their body shapes — and in many cases, just as astonishing.

Dietary Categories

Feeding Type	Description	Example Species
Carnivore	Prey on other animals	Great white shark, barracuda, pike
Herbivore	Feed on algae and plants	Parrotfish, surgeonfish, grass carp
Omnivore	Both plant and animal matter	Carp, tilapia, catfish, bream
Filter Feeder	Strain microscopic organisms from water	Whale shark, manta ray, basking shark
Planktivore	Feed primarily on plankton	Sardine, herring, anchovies
Detritivore	Feed on decaying organic matter	Mullet, loach, many bottom-dwellers
Parasitic	Feed on blood/tissue of hosts	Lamprey, cookiecutter shark
Piscivore	Feed exclusively on other fish	Tuna, pike, grouper, moray eel

Remarkable Feeding Strategies

The archerfish spits water to knock insects from branches. The stonefish lies perfectly camouflaged on the seafloor and lunges at passing prey with a strike lasting just 15 milliseconds — one of the fastest predatory strikes in the animal kingdom. The whale shark, despite being the ocean’s largest fish, feeds exclusively on plankton, krill, and small fish, filtering thousands of litres of water per hour.

Perhaps most remarkable is the cleaner wrasse (Labroides dimidiatus), a small reef fish that sets up “cleaning stations” on coral reefs where larger fish — including natural predators — queue patiently to have parasites, dead tissue, and debris removed from their bodies. It is one of nature’s most striking examples of interspecies cooperation.

Diet Breakdown — General Fish Population

Food Source	% of Fish Species That Consume It
Other fish (piscivory)	~33%
Invertebrates (crustaceans, worms, molluscs)	~55%
Algae and plant matter	~25%
Plankton and microorganisms	~20%
Detritus and organic debris	~15%
Mixed/opportunistic	~30%

(Many species appear in multiple categories as omnivores)

5. Reproduction & Life Cycle

Fish reproduce in a breathtaking variety of ways — a reflection of the extraordinary diversity of environments they have colonized over 530 million years of evolution.

Reproductive Strategies

Oviparity (egg-laying) is the most common reproductive strategy, used by the vast majority of fish. Females release eggs into the water, which are fertilized externally by males — a process called broadcast spawning. A single female Atlantic cod can release up to 9 million eggs in a single spawning event.

Viviparity (live birth) has evolved independently in multiple fish lineages. Many sharks and some bony fish give birth to fully developed young. Some shark species practice intrauterine cannibalism (adelphophagy) — where the strongest embryo consumes its siblings in the womb before birth.

Ovoviviparity — a middle strategy where eggs are retained inside the mother and hatch internally — is used by many sharks, rays, and some bony fish.

Mouthbrooding is one of the more remarkable strategies: many cichlid species hold fertilized eggs — and later, hatched fry — inside their mouths for weeks, protecting them from predators while barely eating themselves.

Life Stages

Stage	Description
Egg	Fertilized; varies from adhesive benthic eggs to free-floating pelagic eggs
Larva	Newly hatched; often transparent, with yolk sac; many look nothing like adults
Juvenile	Increasingly resembles adult form; rapid growth phase
Sub-adult	Approaching sexual maturity; still growing
Adult	Sexually mature; breeding capable
Senescent	Post-reproductive decline in some species

Lifespan Comparison

Species	Average Lifespan	Maximum Recorded
Greenland Shark	250–400 years	500+ years (est.)
Koi Carp	25–35 years	226 years (“Hanako”, Japan)
Rougheye Rockfish	100–150 years	205 years
Atlantic Salmon	4–6 years	~13 years
Clownfish	6–10 years	~30 years
Pygmy Goby	~59 days	~77 days
Great White Shark	40–70 years	~73 years
Goldfish	10–15 years	~43 years

Did You Know? The pygmy goby (Eviota sigillata), a tiny coral reef fish, lives for an average of just 59 days — making it the shortest-lived marine vertebrate on record. On the opposite extreme, the Greenland shark may live over 500 years, meaning some individuals alive today were swimming the Arctic Ocean when Shakespeare was writing his plays.

6. Social Behavior & Communication

Fish are far more socially complex and communicative than most people realize. The popular image of a goldfish with a “three-second memory” and a blank, expressionless face bears almost no relationship to the rich behavioral reality of fish in their natural environments.

Schooling Behavior

Perhaps the most recognizable fish social behavior is schooling — the coordinated movement of large groups of fish in tight, synchronized formations. Schools can number in the millions of individuals (sardine runs off South Africa involve billions of fish) and move with breathtaking coordination, with each fish responding to its neighbors’ movements in real-time.

This synchrony is achieved not through any central “leader” but through each individual fish responding to the movements of the fish immediately around it — a decentralized collective behavior that has fascinated mathematicians, physicists, and biologists alike.

Communication

Fish communicate through a surprisingly rich array of channels:

Sound production — Many fish produce sounds using their swim bladder, specialized muscles, or grinding teeth. The toadfish produces a foghorn-like mating call so loud it disturbed houseboat residents in San Francisco Bay. Drumfish and croakers are named for their vocalizations.
Color signals — Many reef fish display vivid colors that communicate species identity, sex, reproductive status, and dominance — sometimes changing color almost instantaneously.
Bioluminescence — Deep-sea fish use light-producing organs to communicate, attract mates, and lure prey in the absolute darkness of the deep ocean.
Electrical signals — Electric fish like the weakly electric fish of South America (Gymnotiformes) generate and detect low-voltage electric fields for navigation, communication, and mate selection.
Chemical signals (pheromones) — Many fish release chemical signals into the water to indicate alarm, attract mates, or establish territory.

Intelligence and Cognition

Recent research has dramatically revised our understanding of fish intelligence. In 2019, researchers demonstrated that the cleaner wrasse could recognize itself in a mirror — passing the mirror self-recognition test that had previously been considered a benchmark of higher intelligence limited to great apes, dolphins, and elephants. This finding remains controversial but has sparked significant debate about the nature of fish cognition.

Research has also shown that fish can use tools (some wrasse use rocks as anvils to crack open clam shells), demonstrate learned behavior, remember locations and individuals for months, and show signs of anticipatory behavior — planning for future events.

Did You Know? Cleaner wrasse fish have been observed apparently deceiving their clients — eating the protective mucus of visiting fish rather than just parasites — but behaving “correctly” when they observe other fish watching. This implies a level of social awareness that was previously thought impossible in fish.

7. Predators & Defense Mechanisms

The aquatic world is one of perpetual predation — and fish have evolved a spectacular arsenal of defensive strategies to survive it.

Natural Predators of Fish

Larger fish — The primary predators of most fish species; piscivory drives much of the ocean’s food web
Marine mammals — Dolphins, seals, sea lions, whales (for small fish species)
Seabirds — Gannets, pelicans, herons, kingfishers, ospreys
Reptiles — Crocodiles, gharials, sea snakes, marine iguanas
Humans — By far the most significant predator of fish globally

Defense Mechanisms

Camouflage is perhaps the most widespread defense. The stonefish is so perfectly colored to resemble encrusted rock that it is nearly invisible on the reef floor. Flatfish like flounder and sole can change their skin pattern to match any substrate within seconds.

Schooling provides safety in numbers — the confusion of thousands of flashing bodies makes it extremely difficult for a predator to focus on a single individual, a phenomenon called the “confusion effect.”

Venom and spines are deployed by a remarkable range of species. The stonefish carries the most potent venom of any fish — its dorsal spines can inject a toxin capable of killing a human within hours. The lionfish, scorpionfish, and weeverfish all deploy venomous spines as deterrents.

Electricity is the defense of the electric eel (Electrophorus electricus) — which can discharge up to 860 volts, enough to stun a horse.

Inflation — the pufferfish rapidly swallows water (or air) to inflate itself into a near-spherical shape several times its normal size, making it difficult to swallow. Many species are also lethally toxic — tetrodotoxin (TTX) in pufferfish is approximately 1,200 times more poisonous than cyanide.

Mimicry protects many non-toxic species. The harmless mimic filefish resembles the toxic pufferfish. Several reef species have evolved eye-spots near their tails to confuse predators about which end is which.

8. Evolution & Discovery Timeline

The evolutionary history of fish is essentially the story of vertebrate life on Earth. Fish were the first vertebrates — and from their ancient ancestors, every other backboned animal on land eventually evolved.

~530 million years ago (Cambrian Period) — The first jawless, fishlike vertebrates appear in the fossil record. Haikouichthys, discovered in China’s Chengjiang fossil beds, is among the earliest known vertebrates.

~480 million years ago (Ordovician Period) — Armored jawless fish (ostracoderms) proliferate in shallow seas. These are the ancestors of modern lampreys and hagfish.

~430 million years ago (Silurian Period) — Jawed fish (gnathostomes) emerge — a revolutionary development that would shape all subsequent vertebrate evolution. Placoderms — armored jawed fish — become the dominant vertebrates.

~380 million years ago (Devonian Period) — The “Age of Fishes.” Ray-finned and lobe-finned fish diversify explosively. Lobe-finned fish (Sarcopterygii) develop robust, limb-like fins — the ancestors of the legs that would eventually carry vertebrates onto land. The first tetrapods — four-limbed vertebrates — emerge from lobe-finned fish ancestors. The giant placoderm Dunkleosteus — 10 metres long — terrorizes Devonian seas.

~360 million years ago — Tiktaalik roseae, discovered in 2004 in Arctic Canada, is identified as a crucial transitional fossil — a fish with a neck, ribs, and proto-limbs, bridging the gap between fish and the first land vertebrates.

~250 million years ago (Permian-Triassic boundary) — The Great Dying — Earth’s worst mass extinction — devastates marine life but ray-finned fish survive and eventually diversify spectacularly.

~100 million years ago (Cretaceous Period) — Modern fish groups, including many ancestors of today’s species, are well established.

1938 — Living coelacanth discovered off South Africa — the zoological discovery of the century.

1977 — Deep-sea hydrothermal vents discovered, revealing fish and other life forms existing in conditions previously thought incompatible with life.

2003 — Fish genome sequencing begins in earnest; the pufferfish (Takifugu rubripes) becomes the second vertebrate (after humans) to have its genome fully sequenced.

2023 — Snailfish recorded at 8,336 metres depth in the Mariana Trench, shattering the previous depth record for fish observation.

2025–2026 — Continued deep-sea and freshwater surveys reveal new species at a rate of approximately 150–200 new fish species per year globally.

9. Fish & Humans — Historical & Modern Relationship

The relationship between fish and humanity is as old as our species itself — and in many ways, it helped make us what we are.

The Ancient Bond

Archaeological evidence suggests that human ancestors were fishing at least 1.9 million years ago, with systematic fish exploitation well established by 50,000 years ago. Fish provided a rich source of omega-3 fatty acids, proteins, and micronutrients that many researchers believe were crucial to the expansion of the human brain during our evolutionary history.

Coastal and riverine communities worldwide built entire civilizations around fish. The Nile’s annual flood and its extraordinary fish abundance supported ancient Egyptian civilization. The cod fisheries of the North Atlantic fueled the economies of medieval Europe and drove the exploration of North America. The salmon runs of the Pacific Northwest sustained Indigenous cultures for thousands of years.

Modern Fisheries

Today, fish represent the world’s most widely consumed animal protein. Global fisheries production reached approximately 185 million tonnes in 2024, with a combined value exceeding $500 billion. Roughly 3.3 billion people worldwide rely on fish as a primary source of protein.

The industry divides into capture fisheries (fishing wild populations) and aquaculture (fish farming). Global aquaculture production now exceeds wild-capture fisheries for the first time in history — a milestone passed in the mid-2020s.

Fish in Medicine and Science

Fish have contributed to human medicine and science in extraordinary ways:

Zebrafish (Danio rerio) are one of the most important model organisms in biomedical research — their transparent embryos and rapid development make them invaluable for studying genetics, developmental biology, disease, and drug development
Hagfish slime is being studied for applications in bulletproof materials and textiles
Shark cartilage compounds have been investigated (controversially) in cancer research
Pufferfish tetrodotoxin is being researched as a powerful painkiller
Deep-sea fish antifreeze proteins have applications in food preservation and organ transplantation

“The ocean is the lifeblood of Earth, covering more than 70 percent of our planet’s surface. And fish are the ocean’s heartbeat.” — Sylvia Earle, marine biologist and National Geographic Explorer-in-Residence

10. Role in the Ecosystem & Food Chain

Fish are not merely inhabitants of aquatic ecosystems — they are the structural backbone of those systems. Remove fish from the equation, and virtually every aquatic ecosystem on Earth would collapse.

Fish as Primary Consumers

Herbivorous fish like parrotfish and surgeonfish on coral reefs perform a service of incalculable ecological value: grazing on algae that would otherwise smother and kill coral. A healthy population of parrotfish is now understood to be essential for coral reef survival — particularly in the face of climate-driven bleaching events that temporarily kill coral and allow algae to colonize rapidly.

Fish as Apex Predators

Large predatory fish — sharks, tuna, marlin, grouper — regulate the populations of smaller fish and maintain the balance of marine food webs. The removal of apex predators through overfishing causes trophic cascades — chain reactions of ecological disruption that ripple through entire ecosystems.

Fish as Nutrient Cycles

When fish die, their bodies carry marine nutrients into deep water or onto land. Pacific salmon are perhaps the most dramatic example — after spawning, millions of salmon die in rivers, their bodies fertilizing surrounding forests with marine-derived nitrogen and phosphorus. Studies have shown that trees within reach of salmon streams grow significantly faster than those beyond salmon range. Bears, eagles, wolves, and dozens of other species depend on this annual transfer of ocean nutrients to land.

Fish as Prey

Enormous numbers of fish species — particularly small schooling fish like anchovies, sardines, herring, and capelin — serve as critical links between microscopic plankton production and the larger predators (including humans) that depend on them. These “forage fish” are among the most ecologically important animals on Earth, yet they are often overlooked in conservation discussions.

Did You Know? Parrotfish eat coral — literally biting off chunks of reef to access the algae inside — and excrete the calcium carbonate as sand. A single large parrotfish can produce up to 90 kg of sand per year. Many of the world’s most beautiful white sand beaches are, in large part, made of parrotfish excrement.

11. Conservation Status & Threats

The global fish crisis is one of the most serious and underreported environmental emergencies of our time. Across virtually every ocean, river, and lake, fish populations are under extraordinary pressure — and many are declining at alarming rates.

Key Threats

Overfishing is the most pervasive threat. The FAO (Food and Agriculture Organization) estimates that approximately 34% of the world’s marine fish stocks are overfished — meaning they are being harvested faster than they can reproduce — and a further 60% are fished at maximum sustainable limits. Only about 6% of global marine stocks are genuinely underfished.

Habitat Destruction devastates fish populations across all environments. Coral reef degradation (affecting 50% of the world’s reefs since 1950), mangrove deforestation, river damming, wetland drainage, and seabed trawling all destroy critical fish habitat.

Climate Change is now identified as one of the fastest-growing threats. Ocean warming alters species distributions, disrupts spawning cues, bleaches coral reefs, and reduces the oxygen content of seawater. Ocean acidification — driven by increased CO₂ absorption — threatens the shell-forming organisms that form the base of many marine food chains.

Pollution — from agricultural runoff creating dead zones (areas of critically low oxygen), plastic pollution (an estimated 8 million tonnes enters the ocean annually), chemical contaminants, and pharmaceutical waste — degrades water quality across entire river systems and coastal zones.

Invasive Species — often introduced through aquarium releases, ballast water from ships, or deliberate introduction — devastate native fish communities worldwide. The Nile perch introduced to Lake Victoria in the 1950s contributed to the extinction of over 200 endemic cichlid species — one of the largest documented vertebrate extinction events in modern times.

Conservation Status of Key Species

Species	IUCN Status	Population Trend	Primary Threat
Atlantic Bluefin Tuna	Least Concern (recovering)	Increasing (slowly)	Historical overfishing
Whale Shark	Endangered	Decreasing	Boat strikes, bycatch
Great White Shark	Vulnerable	Decreasing	Finning, bycatch
European Eel	Critically Endangered	Decreasing	Habitat loss, overharvest
Sawfish (all species)	Critically Endangered	Decreasing	Bycatch, habitat destruction
Atlantic Salmon	Least Concern (many populations declining)	Decreasing	Dams, pollution, climate
Coelacanth	Critically Endangered	Unknown	Bycatch, habitat
Sockeye Salmon	Least Concern	Variable by population	Climate, dams

Comparison with Related Aquatic Groups

Animal Group	# Species	Conservation Concern Level	Key Shared Threat
Fish	~36,000	Very High	Overfishing, habitat loss
Marine Mammals	~130	High	Bycatch, pollution
Sea Turtles	7	Critical	Bycatch, plastic, habitat

Did You Know? Scientists estimate that 1 in 3 freshwater fish species is currently threatened with extinction — a higher proportion than in most terrestrial vertebrate groups. Freshwater ecosystems cover less than 1% of Earth’s surface but support approximately 10% of all known animal species.

12. Famous Fish in Science, History & Pop Culture

The Coelacanth — discovered alive in 1938 after being assumed extinct for 66 million years, the coelacanth remains the most dramatic zoological rediscovery in history. A second species was discovered off Sulawesi, Indonesia, in 1997.

Jaws (1975) — Steven Spielberg’s film, based on Peter Benchley’s 1974 novel, created a cultural image of the great white shark as a mindless killing machine — an image that drove public fear, shark hunting, and ultimately damaged conservation efforts for decades. Benchley himself later deeply regretted the novel’s impact and became a passionate shark conservationist.

Nemo — the clownfish (Amphiprioninae) shot to global fame following Pixar’s Finding Nemo (2003) and Finding Dory (2016). Tragically, the film’s popularity drove a surge in clownfish purchases, with buyers unaware that most wild-caught clownfish die in captivity — the opposite of the movie’s message.

The Piranha — South American piranhas have been mythologized in popular culture as ferocious killers capable of stripping a cow to bones in minutes. In reality, piranhas are omnivorous scavengers that rarely attack humans unprovoked.

Big Fish (2003) — Tim Burton’s film used fish as a central metaphor for storytelling, memory, and human imagination.

Hanako the Koi — a legendary scarlet koi carp from Japan, reportedly born in 1751 and died in 1977 at the alleged age of 226 years — though this extraordinary claim is based on scale ring-counting and remains debated. Hanako became a symbol of longevity in Japanese culture.

The Blue Planet (2001) and Blue Planet II (2017) — David Attenborough’s landmark BBC documentaries brought the extraordinary diversity and behavior of fish to global audiences and are widely credited with raising public awareness of ocean conservation issues.

13. Myths, Folklore & Cultural Significance

Fish occupy one of the most prominent positions in human mythology, religion, and cultural symbolism of any animal group — rivaled perhaps only by birds and serpents.

Christianity — The fish (Ichthys) is one of the earliest and most enduring symbols of Christianity. Early Christians used the symbol as a covert identifier during periods of persecution. The feeding of the 5,000 with five loaves and two fish is one of the most famous miracles in the New Testament.

Hinduism — Matsya, the fish avatar of Lord Vishnu, is the first of the Dashavatara (ten avatars of Vishnu) — a cosmic fish who saves the first man (Manu) from a great flood. This story predates and parallels the Judeo-Christian Noah narrative.

Ancient Egypt — The Nile tilapia and other fish were both dietary staples and religious symbols. The Nile perch was venerated in some regions, while certain fish species were sacred to specific deities and their consumption was forbidden.

Norse Mythology — Jormungandr, the World Serpent — though technically a serpent rather than a fish — is inextricably linked to the sea and shares mythological space with the great sea creatures of Norse cosmology. The fishing of the giant fish by the god Thor is a central mythological episode.

Chinese Culture — Fish are among the most auspicious symbols in Chinese culture. The word for fish (鱼, yú) sounds identical to the word for abundance/surplus — making fish a ubiquitous symbol of prosperity and good fortune. Koi carp (jinli) represent perseverance, courage, and the ability to achieve goals against all odds — derived from the legend of koi ascending the Dragon Gate waterfall to transform into dragons.

Japanese Culture — The koinobori (carp streamers) flown on Children’s Day (Kodomo no Hi) represent strength and perseverance. The ancient art of gyotaku — fish printing — uses actual fish covered in ink to create detailed impressions, blending fishing culture with artistic tradition.

Indigenous Pacific Cultures — For Pacific Islander peoples across Polynesia, Melanesia, and Micronesia, fish are central to cosmology, subsistence, and identity. Fishing methods, fishing grounds, and specific species hold deep spiritual significance and are governed by complex traditional ecological knowledge systems.

Celtic Tradition — The Salmon of Knowledge (Bradán Feasa) is one of the most important figures in Irish mythology — a fish so ancient it had absorbed all the wisdom of the world. Fionn mac Cumhaill accidentally ate it while cooking and gained all knowledge.

14. Best Places to See Fish in the Wild

The Great Barrier Reef, Australia — The world’s largest coral reef system, stretching 2,300 km along Queensland’s coast, hosts over 1,500 fish species. Snorkeling or diving here is arguably the greatest wildlife spectacle on Earth.

The Galápagos Marine Reserve, Ecuador — Marine iguanas, whale sharks, hammerhead sharks, manta rays, and extraordinary concentrations of reef fish make the Galápagos one of the world’s premier marine destinations. Charles Darwin’s observations here helped shape the theory of evolution.

Komodo National Park, Indonesia — Beyond its famous dragons, Komodo’s surrounding waters host extraordinary fish diversity, including pygmy seahorses, massive schools of fusiliers, and pristine reef systems.

The Amazon River Basin, Brazil/Peru — The world’s most species-rich freshwater ecosystem. River dolphin, arapaima (one of the world’s largest freshwater fish), piranha, electric eel, and thousands of colorful cichlid and characin species inhabit these dark, tea-colored waters.

Lake Malawi/Lake Tanganyika, East Africa — These ancient Rift Valley lakes are evolutionary showcases — each containing hundreds of endemic cichlid species found nowhere else on Earth, many displaying extraordinary colors and behaviors.

Palau, Micronesia — Legendary among divers worldwide for its jellyfish lake, its WWII wrecks teeming with marine life, and some of the most spectacular shark and fish aggregations in the Pacific.

Raja Ampat, Indonesia — Located in the Coral Triangle — the global epicenter of marine biodiversity — Raja Ampat may have more fish species per unit area than anywhere else on Earth.

Monterey Bay, California, USA — World-class marine protected area with remarkable kelp forest ecosystems, hosting sunfish, sevengill sharks, and extraordinary biodiversity accessible to divers and snorkelers.

You may also like: Complete Guide to Coral Reefs | Top 10 Most Endangered Marine Animals | The Ultimate Guide to Sharks

15. How You Can Help

Sustainable Seafood Choices

Check the label — look for MSC (Marine Stewardship Council) or ASC (Aquaculture Stewardship Council) certification when buying fish and seafood
Use Seafood Watch (seafoodwatch.org) — the Monterey Bay Aquarium’s free guide to sustainable seafood choices, available as an app
Reduce consumption of heavily overfished species — Atlantic bluefin tuna, shark fin, certain grouper and snapper species
Choose plant-based alternatives for some meals to reduce pressure on wild fisheries

Support Conservation Organizations

WWF (World Wildlife Fund) — extensive marine and freshwater conservation programs globally
Oceana (oceana.org) — dedicated exclusively to ocean conservation, focusing on policy and fisheries reform
Marine Stewardship Council (msc.org) — promoting sustainable fishing worldwide
Project AWARE (projectaware.org) — diver-led ocean conservation
Shark Trust (sharktrust.org) — focused specifically on elasmobranch (shark and ray) conservation
Trout Unlimited (troutunlimited.org) — freshwater fish and river conservation across North America

Practical Actions

Never release aquarium fish into natural waterways — this is a leading cause of invasive species introduction
Participate in citizen science — platforms like iNaturalist and eShark allow anyone to contribute fish observation data
Reduce plastic use — plastic pollution is devastating aquatic ecosystems globally
Advocate for marine protected areas (MPAs) — support political efforts to expand the network of ocean areas protected from fishing

16. Fun Facts About Fishes

The whale shark is the largest fish on Earth — reaching up to 12 metres in length and weighing up to 21,500 kg — yet feeds almost exclusively on microscopic plankton
Some fish, including certain wrasse and parrotfish, routinely change sex during their lives — females becoming functional males (protogyny) or vice versa (protandry)
The electric eel is not actually an eel — it’s more closely related to catfish and carp than to true eels
Goldfish do not have a three-second memory — research has demonstrated they can remember things for months and can be trained to complete complex tasks
The stonefish is the world’s most venomous fish and can survive out of water for up to 24 hours
Fish were the first vertebrates to evolve jaws — a development so significant it essentially enabled the subsequent evolution of all land vertebrates
The black swallower (Chiasmodon niger) can swallow prey 10 times its own mass — its stomach expands to accommodate fish far larger than itself
Mudskippers — a group of amphibious fish from mangrove habitats — can climb trees, walk on land using their pectoral fins, and breathe through their damp skin
The sailfish (Istiophorus platypterus) is believed to be the fastest fish in the ocean, with burst speeds recorded at over 110 km/h (68 mph)
There are more species of fish than all other vertebrates (amphibians, reptiles, birds, and mammals) combined

17. Frequently Asked Questions About About Fish

Q1: What exactly is a fish — and is it one animal or many?

“Fish” is a collective term for aquatic, gill-breathing vertebrates that do not have four limbs (tetrapods). It is not a single unified group but rather several distinct evolutionary lineages — ray-finned fish, cartilaginous fish (sharks and rays), lobe-finned fish (coelacanths and lungfishes), and jawless fish (lampreys and hagfish). Together, these groups comprise over 36,000 known species — roughly half of all vertebrate species on Earth.

Q2: What is the biggest fish in the world?

The whale shark (Rhincodon typus) is the world’s largest fish, reaching lengths of up to 12 metres and weights of up to 21,500 kg. Despite its enormous size, it is a filter feeder that poses no threat to humans, feeding on plankton, krill, and small fish. The largest bony fish (ray-finned fish) is the ocean sunfish (Mola mola), which can weigh up to 2,300 kg.

Q3: Can fish feel pain?

This question has been intensely debated in science and is increasingly answered with “yes.” Fish possess nociceptors (pain-detecting nerve endings), produce stress hormones when injured, and display protective behaviors in response to harmful stimuli that persist after the immediate threat has passed. The scientific consensus has shifted significantly toward recognizing fish as sentient beings capable of experiencing pain and suffering, though the nature of their subjective experience remains debated.

Q4: How do fish breathe?

Most fish breathe by drawing water in through their mouths and passing it over their gills — highly vascular organs that extract dissolved oxygen from water. Specialized cells in the gill filaments perform gas exchange, absorbing oxygen into the bloodstream while releasing carbon dioxide. Some fish — like lungfishes, mudskippers, and the bowfin — can breathe atmospheric air, using modified swim bladders or simple lungs.

Q5: How many fish species are there?

As of 2026, approximately 36,000 species of fish have been formally described and named. However, scientists estimate that many more remain undiscovered — particularly in deep-sea environments and remote freshwater systems. Approximately 150–200 new fish species are described by science every year.

Q6: Are sharks really as dangerous as movies suggest?

No — and the cultural image of sharks as mindless human hunters is one of the most damaging wildlife myths of the modern era. Worldwide, fewer than 10 people are killed by sharks in an average year — compared to 100 million sharks killed by humans annually through fishing, finning, and bycatch. Sharks are, in ecological terms, far more endangered by humans than humans are threatened by sharks. Most species are completely harmless to people.

Q7: Why are so many fish species threatened with extinction?

The primary drivers of fish population decline are overfishing (approximately 34% of marine stocks are currently overfished), habitat destruction (coral reef degradation, river damming, wetland drainage), climate change (ocean warming and acidification), pollution (agricultural runoff, plastics, chemicals), and invasive species. Freshwater fish are proportionally the most threatened vertebrate group, with an estimated 1 in 3 freshwater species currently at risk.

Q8: Do fish sleep?

Fish do rest, but their sleep is different from mammalian sleep — they lack eyelids and cannot close their eyes. Most fish enter periods of reduced activity and lowered responsiveness that function similarly to sleep, often hovering motionless in a sheltered location. Some species — like parrotfish — secrete a mucus cocoon around themselves at night, possibly to mask their scent from predators while resting. True REM sleep as defined in mammals has not been definitively demonstrated in fish, though some researchers have observed behaviors suggesting something analogous.

18. Sources Researched

Fish Images — shutterstock.com
Wikipedia — en.wikipedia.org/wiki/Fish
National Geographic — nationalgeographic.com
WWF (World Wildlife Fund) — worldwildlife.org
IUCN Red List — iucnredlist.org
Britannica — britannica.com/animal/fish
FAO (Food and Agriculture Organization of the UN) — fao.org (fisheries data)
Smithsonian Ocean — ocean.si.edu
NOAA Fisheries — fisheries.noaa.gov
Monterey Bay Aquarium / Seafood Watch — seafoodwatch.org
FishBase — fishbase.org (the world’s most comprehensive fish species database)
MBARI (Monterey Bay Aquarium Research Institute) — mbari.org
Australian Institute of Marine Science — aims.gov.au
Project AWARE — projectaware.org
Jonathan Balcombe, “What a Fish Knows” (2016)
Rachel Carson, “The Sea Around Us” (1951)