96 Fun Facts About Fish

Roughly how many living fish species are known to science?

About 33,000 species are known, and land animals with backbones, humans included, are really an offshoot of fish that moved onto land.

What is the largest living species of fish?

The whale shark, the biggest fish alive, lives on some of the smallest food, filtering plankton and small fish out of the water it gulps.

Which geological period is nicknamed the 'Age of Fishes'?

The Devonian ended in mass extinctions, and the armoured placoderms that had dominated its waters all but vanished with it.

Which internal organ lets many bony fish adjust their buoyancy?

The swim bladder is a gas-filled sac: by adding or releasing gas, a fish can hold its depth without having to keep swimming.

What is the sensory system that lets fish detect water currents and vibrations called?

The lateral line is a row of pressure-sensing organs, and the blind Mexican cave fish, with no working eyes, relies heavily on it to find its way.

The coelacanth was thought long extinct until a live one was caught off which country in 1938?

In South Africa, museum curator Marjorie Courtenay-Latimer spotted it in a local fisherman's catch, and the genus Latimeria is named after her.

In which fish does the male carry the fertilised eggs in a brood pouch and give birth?

Seahorse fathers slowly change the fluid in the brood pouch from body fluid to seawater as the young develop, readying them for life in the sea.

When the dominant female in a clownfish group dies, what happens?

The breeding male changes sex and takes her place, and the largest non-breeder then becomes the new breeding male.

Up to how many volts can the most powerful electric eel species deliver?

About 860 volts came from Volta's electric eel, described in 2019; despite the name, electric eels are knifefish, closer to catfish than to true eels.

Which toxin makes pufferfish (fugu) potentially deadly to eat?

Tetrodotoxin is believed to come from bacteria in the pufferfish's food, and in Japan only specially trained, licensed chefs may prepare fugu.

Salmon that hatch in rivers, mature at sea and return to spawn are called what?

Anadromous salmon head back to the very stream where they hatched, finding it largely by smell, since its chemistry is imprinted on them when young.

Goldfish were first selectively bred for colour more than 1,000 years ago in which country?

China had domesticated goldfish by the Song dynasty, and pet goldfish released into the wild elsewhere have since become invasive pests.

In a 1994 study, goldfish whose food lever paid out only on a schedule learned to press it when?

Same time each day: the lever fed them for an hour daily, and they learned to anticipate it even under constant light, a sign of an internal clock.

Which fish is the villain of Peter Benchley's 1974 novel Jaws?

A great white shark terrorises the town in Jaws, and Benchley later expressed regret for writing about sharks in a way that fed fear of them.

Which fish can spend long periods out of water on tidal flats, breathing through its skin and mouth lining?

Mudskippers also carry a bubble of air in their enlarged gill chambers, which keeps them breathing while they feed and court on land.

Which Caribbean country is known as 'the land of the flying fish' and puts it in its national dish?

Barbados's flying fish don't really fly: they build up speed underwater, burst through the surface and glide on their outspread fins.

In deep-sea anglerfish, what did scientists first mistake the tiny males for?

The 'parasites attached to the female' were males that bite on, fuse with her skin and share her bloodstream, depending on her for food from then on.

Which fish produces more eggs at a time than any other known vertebrate, up to 300 million?

The ocean sunfish is thought to be named for basking at the surface, which may help it warm up after deep, cold dives.

Which US president helped cement the piranha's fearsome reputation after a 1913 trip to Brazil?

He described them as vicious creatures in his 1914 book Through the Brazilian Wilderness.

Which fish, once estimated at 125 km/h, is often cited as the fastest in the ocean?

Sailfish lost much of that record in a 2016 muscle study, which found such speeds unlikely and estimated a top speed of only about 30 km/h.

Which shark can live in fresh water and has been found far up the Amazon River?

Bull sharks can live in fresh water, and haunting shallow waters close to people may make them the most dangerous shark to humans.

Caviar is traditionally the processed roe of which fish?

Sturgeon caviar was relatively cheap and common until sturgeon stocks began to collapse in the late 19th century, turning it into a luxury.

The giant oarfish, the longest bony fish, may lie behind old sightings of what?

Sea serpents: oarfish are ribbon-like and very long, and they drift near the surface or wash ashore when sick or dying, which may explain the legends.

The betta, a popular aquarium fish, is the national aquatic animal of which country?

Thailand has long bred bettas for fighting, and its government named the fish a national animal in 2019, citing its historical and cultural significance.

Koi are often mistaken for oversized goldfish, but they are coloured varieties of which fish?

Carp farmers in Niigata's snowy mountains kept the fish as winter food, and from the early 19th century they bred the colourful ones for show.

A remora clings to sharks and whales using a suction disc that evolved from which body part?

Its first dorsal fin evolved into the ridged sucking disc, and a riding remora is thought to feed on scraps from its host's meals.

Which English king is said to have died from eating 'a surfeit of lampreys'?

Henry I's death in 1135 was long blamed on the lampreys, but historians doubt it, and a 2023 medical review proposed a Listeria infection instead.

Which fish has one of the largest brains for its body size and may recognise itself in a mirror?

Manta rays also visit reef cleaning stations, holding still for minutes while small fish pick off their parasites, and many return to the same station.

What is generally regarded as the most venomous fish in the world?

Stonefish are camouflaged so well as rocks or coral that people rarely see them, and the venomous spines on their backs can deliver fatal stings.

Which shark, thought to live for several centuries, has the longest known lifespan of any vertebrate?

Greenland sharks were aged by radiocarbon-dating the lenses of their eyes, which suggested females take about 150 years to reach maturity.

Swordfish have special 'heater' tissue that warms which organs, helping them hunt in cold water?

Their eyes and brain are warmed by a special tissue linked to one of the eye muscles, which helps them spot fast-moving prey.

How does a hagfish escape after covering a predator's gills in slime?

It knots itself and slides the knot along its body, stripping off its own slime so that it doesn't suffocate in it.

The barreleye is a deep-sea fish whose tubular eyes sit inside what?

A transparent dome on its head lets its tubular eyes rotate to look up or forward, and may shield them from stinging siphonophores it is believed to steal food from.

European eels travel thousands of kilometres to spawn in which body of water?

The Sargasso Sea is where they spawn and then die, and their larvae drift all the way back to Europe on the Gulf Stream.

A shark's skeleton is made mostly of what?

Cartilage is much lighter than bone, which helps sharks stay afloat along with their large, oil-filled livers, since most must keep swimming or sink.

The arapaima, an Amazon giant reaching 3 metres, must regularly surface to do what?

Arapaima breathe air through a lung-like organ, and having to surface to breathe makes them easy targets for fishers with harpoons.

Antarctic icefish are the only known vertebrates that, as adults, lack what?

Hemoglobin-free icefish get by with bigger hearts and extra blood volume, drawing enough oxygen from the Southern Ocean's cold, oxygen-rich water.

Which small fish is a standard lab model because its embryos are transparent and develop outside the mother?

Zebrafish can also regrow damaged fins, spinal cord, retina and even heart tissue, which makes them a leading model for regenerative medicine.

Where was Tiktaalik, the famous 'fishapod' fossil, discovered in 2004?

Ellesmere Island, Canada, is now Arctic, but when Tiktaalik lived there about 375 million years ago it lay much farther south, with a warm climate.

Which country fought the 20th-century 'Cod Wars' with the United Kingdom over fishing rights?

Iceland prevailed by threatening to close the NATO base at Keflavik and leave NATO, and in 1976 Britain accepted its 200-mile fishing zone.

Which venomous Indo-Pacific reef fish has become an invasive pest in the Caribbean and western Atlantic?

Lionfish have few or no predators in the Atlantic and breed rapidly, so they eat and outcompete native reef fish.

Which popular food fish is also known as the dolphinfish?

Mahi-mahi gather under floating objects, so some fishers set out floating mats of palm leaves or bamboo to draw them in before netting.

How do African lungfish survive when their pools dry up?

They burrow into mud and seal themselves in a mucus cocoon that hardens, waiting there until the dry season ends.

The opah is warm-blooded throughout its body; what generates most of that heat?

Its swimming muscles make the heat, and a heat-exchanging network of blood vessels in its gills keeps that warmth from escaping into the cold water.

Hagfish and sharks, which often find food in murky or dark water, have very large versions of what?

Olfactory lobes process smell, and hagfish, whose eyes can't form images, bore into dead and dying animals to eat them from the inside.

How do most fish get rid of their nitrogenous waste?

As ammonia: it is toxic but dissolves so readily that most fish can simply pass it out across their gills into the surrounding water.

Much of the fine sand on tropical beaches is coral ground up and excreted by which reef fish?

Parrotfish scrape rock from the reef with a beak of tightly packed teeth, digest the edible parts and excrete the rest as sand, which helps to build beaches and even small islands.

Sweden's navy once hunted 'Soviet submarines' whose sounds were probably gas released by which fish?

Herring pass gas in noisy bursts, which experts later judged the likeliest cause of the navy's recordings. The study showing they apparently communicate by farting won an Ig Nobel Prize.

Which deep-sea fish from the waters off Australia was voted the world's ugliest animal in a 2013 online poll?

Blobfish flesh is a gelatinous mass slightly less dense than water, so the fish floats just above the sea floor without spending energy on swimming.

In Pixar's Finding Nemo, the forgetful Dory voiced by Ellen DeGeneres is which kind of reef fish?

Blue tang is the short name for the regal blue tang, which carries a spine in a groove at the base of its tail. A reported rush to buy the film's fish as pets was dubbed the 'Nemo effect'.

McDonald's Filet-O-Fish was created by a Cincinnati franchisee whose burger sales slumped on which day?

Friday was a meat-free day for his mostly Catholic customers. The sandwich earned its menu spot by outselling Ray Kroc's rival idea, the Hula Burger: grilled pineapple and cheese in a bun.

Which small fish goes into traditional Worcestershire sauce alongside vinegar, molasses and tamarind?

Anchovies are the reason the fermented sauce is off limits to vegetarians and people with fish allergies. English cooks were already mixing them into sauces in the seventeenth century.

In which country do April Fools' Day pranksters traditionally try to stick a paper fish on someone's back?

France knows an April fool as a 'poisson d'avril', literally April's fish, a phrase the poet Eloy d'Amerval was already using in 1508.

In Ernest Hemingway's The Old Man and the Sea, the fisherman Santiago battles for days with which giant fish?

Marlin, in this case one measured at eighteen feet and longer than Santiago's boat. He lashes it alongside, but sharks strip it to a skeleton before he reaches home.

Which fish fatally wounded 'Crocodile Hunter' Steve Irwin while he filmed an underwater documentary in 2006?

Stingray deaths are so rare that Irwin's, from a short-tail stingray's barb to the chest, is believed to be the only one ever captured on video.

Hawaii's state fish, the humuhumunukunukuāpuaʻa, is named for having a snout like which animal?

A pig is also what the reef triggerfish sounds like, because it grunts when it is held out of the water. It lost its state title in 1990 and was permanently reinstated in 2006.

'Chilean sea bass' is a menu name a wholesaler invented in 1977 for which less appealingly named fish?

Patagonian toothfish got its new name from wholesaler Lee Lantz, who weighed up 'Pacific sea bass' and 'South American sea bass' first. US regulators accepted his choice as a market name in 1994.

Despite its name, South America's electric eel is not a true eel but a member of which group of fishes?

Knifefish are mostly only weakly electric, using their fields to sense their surroundings. Electric eels are the branch of the group that evolved shocks strong enough to stun.

Which reef predator has a second set of jaws in its throat that shoots forward to drag prey down?

Moray eels are the only animals known to catch and restrain prey with throat jaws. The mouth bites first, then the second set, complete with tiny teeth, reaches up to pull the meal back.

Which bottom-feeding fish has taste receptors across its entire body, so that it tastes anything it touches?

Catfish lean on taste and smell so heavily to find food that their eyes are generally small, and some species that moved into underground waters have lost them entirely.

A male betta, the popular aquarium fish, guards his eggs in a floating nest that he builds from what?

Bubbles hold the eggs at the surface, and the male uses his mouth to put back any that sink. He has reason to hurry: the female often eats every egg she can catch.

Goldfish produce unusually large amounts of waste for their size because they lack which digestive organ?

A stomach is something goldfish simply do not have, and the heavy waste that results is one reason they need a large volume of well-filtered water instead of a small bowl.

Which small aquarium fish, also called the millionfish, gives birth to live young instead of laying eggs?

Guppy is the surname of Robert John Lechmere Guppy, who sent specimens from Trinidad to London's Natural History Museum. The fish has since been released around the world to eat mosquito larvae.

Which famous thinker spent weeks in 1876 dissecting hundreds of eels in a failed search for their testes?

Sigmund Freud was then a student at a zoological research station in Trieste, years before he turned to psychoanalysis, and his hunt for the male organs ended inconclusively.

Which of these fish starts life swimming upright before one eye migrates across its head to join the other?

Halibut are flatfish, born symmetrical with an eye on each side. After about six months one eye moves over, and the adult lies on the seabed with its blind side down.

The glowing lure that dangles in front of a deep-sea anglerfish gets its light from what living inside it?

Bacteria that glow live in the tip of the lure, called the esca, which sits on the end of a modified fin ray. Not every anglerfish has them: sea toads carry the rod but no light.

Pearl essence, which gives shimmer to some nail polish, was first extracted from which part of a fish?

Scales of the freshwater fish Alburnus alburnus yielded the first pearl essence in Paris in 1656. It is crystalline guanine, which is also used to make simulated pearls.

In the Latin American dish ceviche, raw fish turns firm and opaque without heat after marinating in what?

Citrus juice, typically lime or lemon, carries acid that alters the proteins in the flesh. Before the Spanish brought citrus fruit to the Andes, coastal cooks used the juice of banana passionfruit.

Scandinavian lutefisk is dried whitefish that takes on a gelatinous texture after it is cured in what?

Lye saturates the fish to a pH of 11 or 12, which leaves it inedible until another four to six days of soaking in cold water make it ready to cook.

Imitation crab sticks, the seafood counter staple, are usually made from the minced flesh of which fish?

Alaska pollock from the North Pacific is pulverised into a paste called surimi, mixed with starch, then shaped and cured to resemble the leg meat of a snow crab.

A single fish of which species sold for about $3.1 million at a Tokyo New Year auction in 2019?

Bluefin tuna fetch inflated prices at the year's first auction because winning it brings publicity, so this 618-pound fish went for far more than its usual market value.

Which freshwater fish, farmed in many parts of the world, is known around the Sea of Galilee as 'St. Peter's fish'?

Tilapia owe the name to a story in the Gospel of Matthew in which the apostle catches a fish carrying a coin in its mouth. The passage itself never names the species.

Which South American cousin of the piranha has squarer teeth and crushing jaws for eating seeds and nuts?

Pacu caught in the strait between Sweden and Denmark set off media warnings that the fish attacks testicles. The claim began as a joke about its taste for tree nuts.

Which invasive Asian fish, nicknamed 'Frankenfish' in America, can wriggle across wet land to reach new ponds?

Snakehead fish can survive out of water for up to four days as long as they stay wet, and are known to cross as much as 400 metres of land between one body of water and the next.

Which African lake holds more fish species than any other lake on Earth, most of them cichlids?

Malawi has at least 700 species of cichlid, nearly all of them found nowhere outside the lake system. Their bright colours have made them favourites with aquarium owners.

Fossil teeth as long as a human hand are the best-known remains of which extinct sea giant that hunted whales?

Megalodon means 'big tooth', and its teeth could top 18 cm, the largest of any known shark. Its skeleton was too soft to fossilise well, so the animal's true size and shape are uncertain.

Which Central American country's Yoro region holds a yearly festival celebrating a mysterious 'rain of fish'?

Honduras has held the Festival de Lluvia de Peces since 1998, timed to the first big rains of May or June. Many locals credit the prayers of a nineteenth-century Spanish priest; scientists suspect waterspouts.

Trout tickling, a poacher's trick mentioned in Shakespeare's Twelfth Night, lands the fish using nothing but what?

Bare hands are enough: the tickler strokes along the trout's belly towards the gills, then grabs it and throws it onto the bank. Poachers liked a method that needed no incriminating nets, rods or lines.

The 'salmon cannon', a pneumatic tube that fires live fish through the air, was built to carry them over what?

Dams block the fish's route upstream to spawn, so the tube sucks them in one at a time and shoots them over. Its makers first built the system to move apples gently from orchard trees to bins.

In the Hebrew Bible, which reluctant prophet spends three days and three nights in the belly of an enormous fish?

Jonah is usually pictured inside a whale, but the Hebrew text says only 'large fish'. He was thrown overboard in a storm while fleeing God's command to preach in Nineveh.

'A woman needs a man like a fish needs a…': which word completes the slogan popularised by Gloria Steinem?

Bicycle ends a line coined by the Australian activist Irina Dunn. When Time magazine credited the saying to Steinem, Steinem wrote in to say that Dunn had come up with it.

The mechanical sharks built for Steven Spielberg's Jaws were nicknamed 'Bruce' by the crew after his what?

His lawyer was Bruce Ramer. The three prop sharks broke down so often, partly from salt water in their hoses, that Spielberg chose mostly to suggest the shark's presence instead of showing it.

In which US city do Pike Place Fish Market's fishmongers throw every order across the stall before wrapping it?

Seattle's best-known fish stall was close to bankruptcy in 1986 when its staff set out to make it 'world famous'. The throwing, chanting and games with customers that followed drew national media.

Which bright star, whose Arabic-derived name means 'mouth of the fish', marks the constellation Piscis Austrinus?

Fomalhaut is the brightest star in the Southern Fish. A suspected planet beside it was named Dagon, after an ancient god often shown as half man, half fish, before it proved to be a cloud of debris.

Which London fish market, once the world's largest, became a byword for coarse and abusive language?

Billingsgate fishmongers were notorious for swearing: a chronicle by Raphael Holinshed was already grumbling in 1577 about the foul tongues of the market's oyster-wives.

Which English writer's The Compleat Angler, first published in 1653, celebrates the art of fishing in prose and verse?

Izaak Walton cast it as a dialogue between a veteran angler, Piscator, and his pupil, and went on adding to the book for a quarter of a century.

Which Harvard naturalist, a champion of the Ice Age theory, made his name with five volumes on fossil fish?

Louis Agassiz published his Recherches sur les poissons fossiles between 1833 and 1843. In 1837 an audience expecting a lecture on fossil fish heard him unveil his theory of a past ice age instead.

In Hindu tradition, Matsya, the fish that saves the first man from a flood, is an avatar of which god?

Vishnu's fish form is often counted as the first of his ten main avatars. In the story a tiny fish that Manu shelters grows huge, then tows his boat through the deluge by its horn.

Goldfish crackers, sold in America by Pepperidge Farm, were invented by a biscuit maker in which European country?

Switzerland's Kambly bakery created the fish-shaped snack in 1958 for its owner's wife, who was a Pisces. Pepperidge Farm's founder Margaret Rudkin tried the crackers on holiday and took the idea home.

Stargazy pie, baked with fish heads poking through the crust as if gazing at the sky, comes from which English county?

Cornwall's village of Mousehole eats the pie on Tom Bawcock's Eve, honouring a fisherman said to have braved a winter storm and landed enough fish to save his neighbours from starvation.

Which Austrian composer's 'Trout' Quintet is nicknamed after his own song about a fish, reused in its fourth movement?

Schubert wrote the quintet for Sylvester Paumgartner, a wealthy amateur cellist who suggested he work in a set of variations on 'Die Forelle', his earlier song.

Which British artist suspended a tiger shark in a tank of formaldehyde for a much-debated 1991 artwork?

Damien Hirst had the 14-foot shark caught to order off Queensland. Poorly preserved, it decayed and clouded its liquid, and it was replaced with a new specimen in 2006.

Big Mouth Billy Bass, the animatronic wall-mounted fish, sings 'Don't Worry, Be Happy' and which Al Green song?

Take Me to the River earned its co-writer Teenie Hodges more royalties from the singing fish than from any other recording of the song. Elizabeth II reportedly kept one on a piano at Balmoral.

Which branch of zoology, whose 'father' Peter Artedi worked alongside Carl Linnaeus, is devoted to the study of fish?

Ichthyology got its system for grouping fishes from Artedi, who drowned in a canal at 30. Linnaeus, as the two friends had agreed, finished his manuscripts and saw them into print.

Which American children's author wrote the rhyming beginner book One Fish, Two Fish, Red Fish, Blue Fish?

Dr. Seuss published it in 1960, and by 2001 it had sold more than six million copies, ranking 13th on Publishers Weekly's list of all-time bestselling children's books.

Three of these sea creatures are invertebrates with misleading names; which one is a true fish related to rays?

Sawfish are very large rays whose long snout is lined with teeth like a saw, and some species grow to about 7 metres. Starfish, cuttlefish and jellyfish have no backbone at all.