50 Fun Facts About Fish

Roughly how many living fish species are there, more than all other vertebrates combined?

About 96% of them are teleosts, the ray-finned group that can protrude its jaws.

What is the largest living species of fish?

Despite its size it is a filter feeder that eats plankton, krill and small schooling fish; the largest reliably measured individual was 18.8 metres long.

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

Placoderms, lobe-finned fish and early sharks all diversified then, roughly 420 to 360 million years ago.

Which internal organ lets many bony fish adjust their buoyancy?

Lungs in land animals are homologous with it; some fish can even detect sound through it.

What is the sensory system along a fish's flanks that detects currents and vibrations called?

Blind cave fish navigate almost entirely by it.

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

It is the classic Lazarus taxon; a second species was later found in Indonesian waters.

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

The female can deposit up to 1,500 eggs, and the male carries them for 9 to 45 days.

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

Clownfish live in a size-based hierarchy with the female on top; everyone else moves up one rung.

Up to how many volts can an electric eel deliver?

Despite the name it is a knifefish, not a true eel, and it uses three separate electric organs.

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

Bacteria in the fish's gut are now thought to be the source; only specially trained chefs may prepare fugu in Japan.

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

They return primarily to their natal streams; young 'parr' spend six months to three years there before becoming silvery 'smolts'.

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

Red and orange mutations of grey carp were first recorded during the Jin dynasty; the fish reached Japan centuries later.

How long is a goldfish's memory span, contrary to the popular myth?

They can also tell apart different shapes, colours and sounds.

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

Its triangular teeth reach 7.5 cm, and its jaws are connected to the skull only by muscle and tendon so they can thrust forward.

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

They defend territories and court partners on land, and keep an air pocket in their burrows when the tide comes in.

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

The national dish is cou-cou and flying fish.

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

The male fuses to the female's body; an unusual immune system is what allows the two to merge.

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

Genetic analysis found the sunfish is a generalist predator: jellyfish make up only around 15% of its diet.

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.

How does the archerfish catch insects sitting on leaves above the surface?

They can knock down prey up to 3 metres above the surface, aiming at angles between 45 and 110 degrees.

Which fish, once estimated at 125 km/h, is widely considered the fastest in the ocean?

Research in 2015 and 2016 cut the estimate to a still-brisk 35 to 55 km/h.

Paedocypris progenetica, one of the smallest known fish, has an average length of roughly what?

It lives in Indonesian peat swamps and weighs between 4 and 16 milligrams.

Caviar is traditionally the processed roe of which fish?

In the 19th century the United States controlled about 90% of the world caviar trade.

The largest one on record, a 7.2-metre beluga, was caught in 1827 in the delta of which river?

It weighed 1,571 kg; sturgeon lineages go back to the Early Jurassic.

The Siamese fighting fish, or betta, is the national aquatic animal of which country?

Its labyrinth organ lets it gulp air at the surface, which is why it survives in tiny bowls.

Ornamental koi breeding began in the early 19th century in which Japanese region?

The Japanese word nishikigoi means 'brocaded carp'.

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

Sliding backward increases the suction; swimming forward releases it.

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

Lampreys are jawless fish, more closely related to hagfish than to any jawed vertebrate.

Which fish has the largest brain of any fish and may recognise itself in a mirror?

The giant oceanic species reaches 7 metres across; their brains even have heat-conserving networks of blood vessels.

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

Its stings can kill a human if untreated; the fish looks like an encrusted rock on the seabed.

Which species has the longest known lifespan of any vertebrate, estimated at 272 to 510 years?

They are thought to reach sexual maturity at around 150 years old, and their toxic flesh is fermented into the Icelandic dish hákarl.

Swordfish have special 'heater cells' next to which organs?

Warming the eyes and brain 10 to 15 °C above the water sharpens their vision when hunting; adult swordfish also lose all their teeth and scales.

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

Hagfish are jawless, and their loose skin holds close to a third of their blood.

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

The dome likely protects the eyes from the stinging cells of siphonophores, from which the fish is thought to steal food.

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

Dutch researchers once used a swimming machine to simulate the 6,500 km journey in an attempt to breed them in captivity.

A shark's skeleton is made mostly of what?

It is about half the density of bone; a big oily liver full of squalene helps with buoyancy instead of a swim bladder.

Roughly how many teeth can some sharks lose over a lifetime?

Replacement rows grow in a groove inside the jaw and move forward like a conveyor belt.

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

Its enlarged swim bladder is lined with lung-like tissue, an advantage in oxygen-poor water.

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

Their blood is colourless; remnants of the hemoglobin genes still sit in their genome.

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

The 'Casper' strain was bred to stay transparent into adulthood, and the species is famous for regenerating tissue.

The four-eyed fish Anableps actually has how many eyes?

Each eye is divided so the fish can see above and below the surface at once while cruising with its eyes at water level.

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

It lived about 375 million years ago, when the island sat near the equator with a warm climate.

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

Cod livers are also processed into cod liver oil, a source of vitamins A, D and E and omega-3s.

Roughly what share of living fish species are ray-finned fishes of the class Actinopterygii?

Teleosts, the bony fish able to protrude their jaws, account for about 96% of all fish species.

How many loops does a fish's circulatory system have, compared with a mammal's two?

The heart pumps blood through the gills and on around the body in a single circuit.

Roughly how many fish species can breathe air, letting them live in oxygen-poor water or on land?

Bichirs and lungfish have tetrapod-like paired lungs and must surface to gulp air.

Which lampriform fish is warm-blooded throughout its whole body, heated by its swimming muscles?

Most fish are ectothermic, though tunas and billfishes are also endothermic.

In which geological period did jawed vertebrates such as the armoured Dunkleosteus first appear?

Cartilaginous and bony fish both also emerged during the Silurian, before the Devonian 'age of fishes'.

Fish that hunt mainly by smell, such as sharks and hagfish, have very large versions of what?

Sight hunters like rainbow trout instead have enlarged optic lobes in the midbrain.

How do most fish get rid of their nitrogenous waste?

It leaves through the gills or the kidneys, while a rectal gland handles excess salt.