Aquarium Fish Trivia
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49 free Aquarium Fish trivia questions with answers — nature quiz, new questions added Sep 2026.
This aquarium fish trivia quiz is for anyone who has ever stood in front of a tank and wondered. It covers the classics of the hobby — goldfish and their surprisingly long memories, bettas and their bubble nests, guppies, platies and swordtails, neon and cardinal tetras, angelfish, discus, oscars, corydoras, plecos, gouramis, barbs and loaches — plus the marine stars made famous by Finding Nemo, and the koi, shrimp and rasboras that round out a fishkeeper's world. It also digs into the science and history behind the glass: who coined the word aquarium, how the nitrogen cycle works, why bowls became a thing, what a refugium is, and which fish became a lab model organism. About a third of the questions are easy warm-ups; the rest will test people who know their Poeciliidae from their Loricariidae. If you like this one, our general fish trivia and jellyfish pages go further afield. Every answer has been checked against Wikipedia's species and fishkeeping articles and the sources they cite, and each explanation adds one more thing worth knowing.
30 of 49 questions with answers and explanations. Play the quiz
Q 01The world's first public aquarium opened in 1853 at which zoo?
London Zoo
London Zoo's Fish House was stocked by the naturalist Philip Henry Gosse, whose 1854 book The Aquarium gave the word its modern meaning and set off a Victorian craze for keeping tanks at home.
Q 02The bala shark sold for home aquariums is no shark at all but a relative of which fish?
Carp
Carp are its kin: the bala shark owes its name only to a torpedo-shaped body and tall fins, and as a shoaling fish that reaches 35 cm it soon outgrows most home tanks.
Q 03Some of the earliest known fishkeepers were which ancient people, around 2500 BCE?
Sumerians
Sumerians kept fish in artificial ponds at least 4,500 years ago; the Romans later did the same with sea fish, in ponds supplied with fresh seawater.
Q 04The goldfish was first bred for colour more than 1,000 years ago in which country?
China
China's breeders started from a dull, olive-grey pond fish with the odd golden mutant; let goldfish loose in a river and within generations they revert to that wild colour and can reach 30 cm.
Q 05A popular myth, long since disproved, says a goldfish's memory lasts only how long?
Three seconds
Three seconds is the myth; in tests goldfish learn which paddle earns food, escape nets and run mazes, and can still repeat the tricks weeks or even months later.
Q 06Which venomous aquarium fish from the Indo-Pacific has overrun Caribbean reefs, probably after owners dumped their pets?
Lionfish
Lionfish have very few predators in the Atlantic and eat the young of snapper and grouper, so divers in Florida and Texas are encouraged to spear them for sport and for the table.
Q 07The Bubble Eye goldfish is distinguished by fluid-filled sacs under its eyes and the lack of which fin?
Dorsal fin
Dorsal fin missing, the Bubble Eye struggles to keep its balance, and its sacs are easily sucked against a filter intake; a damaged sac usually grows back, though not always the same size.
Q 08Which aquarium fish knocks insects off overhanging leaves with a jet of water spat from its mouth?
Archerfish
Archerfish aim from below the surface, so they have to allow for the way light bends between water and air, and they can still hit an insect more than a metre above them.
Q 09Which organ lets bettas gulp air and survive poorly oxygenated water?
The labyrinth
The labyrinth is a chamber of folded, bony plates above the gills that takes oxygen from gulped air; many of these fish rely on it so heavily that they must reach the surface to survive.
Q 10What do male bettas build at the surface of the water to hold their eggs?
A bubble nest
A bubble nest keeps the eggs at the surface, where oxygen is richest; the male gathers each sinking egg, lodges it among the bubbles and guards the raft until the fry hatch.
Q 11The guppy is named after Robert John Lechmere Guppy, who sent specimens to London from which island?
Trinidad
Trinidad was home to Robert Guppy, an engineer and schools inspector rather than a career zoologist; the fish already had a scientific name from Venezuela, so his surname survived only as its everyday name.
Q 12Guppies, mollies, platies and swordtails are all what kind of fish?
Livebearers
Livebearers give birth to free-swimming young instead of laying eggs, and a female can store sperm for months, so a single mating can yield a new brood roughly every four weeks.
Q 13What is the gonopodium of a male guppy or platy?
A modified anal fin used for mating
Q 21Clownfish are protandrous hermaphrodites, meaning what?
A male can change into a female
A male can change into a female, never the reverse: every clownfish starts out male, and only when a group's dominant female is lost does her mate switch sex to take her place.
Q 22Dory in Finding Nemo is which species, a favourite of marine aquarists?
Regal blue tang
Regal blue tang in shops are still mostly taken from wild reefs rather than bred; cornered, the fish raises a razor-sharp, venomous spine on either side of its tail.
Q 23Which large South American cichlid, also called the velvet or marble cichlid, is eaten as food in its homeland?
Oscar
A modified anal fin used for mating, the gonopodium is rolled into a tube that passes bundles of sperm to the female; her own anal fin stays fan-shaped, the quickest way to tell the sexes apart.
Q 14The 'sword' of the swordtail, a long spike on the lower edge of the tail fin, is grown by which fish?
Adult males only
Adult males only, because females choose mates with longer swords, even though a long sword also makes its owner easier for predators to spot; the female is the bigger fish but has none.
Q 15The platy crosses so readily with which close relative that most shop fish are said to be hybrids of the two?
Swordtail
Swordtail and platy belong to the same genus and cross so freely that few aquarium strains are pure, which also made the pair standard subjects for genetics research.
Q 16The neon tetra, one of the most widely kept tropical fish, is native to which river basin?
The Amazon
The Amazon's acidic forest streams are its home, yet few shop neons have ever seen them: the great majority on sale are bred on commercial farms rather than caught.
Q 17How can you tell a cardinal tetra from a neon tetra?
Its red runs the whole body length
Its red runs the whole body length, where a neon's stops about halfway; and while shop neons are farm-bred, many cardinals on sale were still caught wild in tributaries of the Rio Negro.
Q 18Which tall, flat-sided cichlid with sail-like fins and dark vertical bars is a mainstay of tropical aquariums?
Angelfish
Angelfish pair up and spawn on a vertical surface such as a broad leaf, or the aquarium glass or filter pipe if nothing better is on offer, then stand guard over the eggs and fry.
Q 19Discus fish feed their newly hatched fry on what?
Mucus secreted from their own skin
Mucus secreted from their own skin is the fry's first food: they graze it straight off their parents' sides while both adults stand guard over the brood.
Q 20Clownfish live unharmed among the stinging tentacles of which animal?
Sea anemone
Sea anemone stings that would kill other small fish are blunted by a protective coating the clownfish wears; in return the fish drives off intruders and keeps its host clean.
Oscar is esteemed on the table across tropical South America and sold in local markets, yet it grows too slowly to be worth farming, so it is the aquarium trade that made its name.
Q 24What protects Corydoras catfish along each flank in place of scales?
Overlapping armour plates
Overlapping armour plates of bone run in two rows down each side; corys also dash to the surface to swallow air, which they absorb through the gut, so they cope in water short of oxygen.
Q 25The common pleco is bought by hobbyists mainly for what job?
Cleaning algae as a bottom cleaner
Cleaning algae as a bottom cleaner comes naturally to a suckermouth catfish: the mouth clamps on to glass, rock or wood and rasps off whatever is growing there.
Q 26Bristlenose or bushynose plecos belong to which genus?
Ancistrus
Ancistrus comes from the Greek for 'hook', after the males' curved cheek spines; it is also the males that grow the fleshy tentacles on the head, and that guard the eggs in a cave.
Q 27GloFish, the fluorescent pets that reached American shops in 2003, were first engineered from which common aquarium fish?
Zebra danio
Zebra danio made to glow were among the first genetically engineered animals sold to the public; the FDA waved them through in December 2003, reasoning that aquarium fish are not eaten.
Q 28Koi breeding for colour began in the early 19th century in the hill villages of which Japanese prefecture?
Niigata
Niigata's hill farmers kept plain black fish in ponds as winter food; when the odd coloured mutant turned up they prized it and bred from it, and a century later the results were being called 'brocaded' koi.
Q 29Hanako, a scarlet koi that died in Japan in 1977, was claimed from her scale rings to have reached what age?
226 years
226 years is the age claimed for her when she died, from rings counted on her scales like those of a tree; the count was never published, and an ichthyologist asked about it said scales are the least accurate way to age such a fish.
Q 30Many African lake cichlids protect their eggs and fry by carrying them where?
In the mother's mouth
In the mother's mouth the eggs hatch and the fry stay for up to three or four weeks; she barely eats in that time, and a brooding female can be spotted by her bulging jaw.