Freshwater Fish
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50 free Freshwater Fish trivia questions with answers — trivia quiz, new questions added Oct 2026.
Rivers, lakes and ponds hold only a tiny fraction of the planet's water, yet they are home to an astonishing share of its fish. Some are bruisers longer than a rowing boat, some are bright slivers that fit on a fingertip, and plenty have habits nobody would believe without the footage: fish that hunt birds, breathe air, survive for days on dry land or raise their young in the strangest places. This quiz covers the whole freshwater world. Expect the game fish that anglers chase across North America and Europe, the tropical species that fill home aquariums, the invaders that have upended famous lakes, and the quirks of biology that let a fish live where the water is still, warm or short of oxygen. There are questions on records, rare species and conservation fights, and a few on the books, music and films that fishing has inspired. It is written for anglers, fishkeepers, students and anyone who enjoys a good nature quiz. The opening questions are the friendliest, the later ones will test people who really know their species, and every answer comes with a short explanation, so you finish knowing more than when you started.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which famous thinker, as a young student, dissected hundreds of eels in a failed hunt for their male sex organs?
Sigmund Freud
Sigmund Freud conceded failure in his first major research paper and turned to other subjects. The organs were not seen until some 20 years later, in an eel caught off Sicily.
Q 02Wels, the giant fish introduced to France's River Tarn, have been filmed lunging onto the bank to snatch which birds?
Pigeons
Pigeons bathing at the water's edge were caught in 28% of the lunges that Toulouse researchers filmed. The trick has never been reported in the native range of the wels, so it seems to be a new habit.
Q 03In the American South, 'noodling' means catching which fish with bare hands by reaching into its underwater hole?
Catfish
Catfish guarding eggs in a hole will latch onto a hand pushed inside, and the noodler hauls the fish out by it. The sport is now illegal in some states where it was once a tradition.
Q 04In much of Central Europe, which fish is the traditional Christmas Eve dish, often kept in the bathtub for days first?
Carp
Carp is kept in the bathtub to flush out its muddy taste, then usually breaded and fried. Czechs and Slovaks slip one of its scales under a plate or into a wallet as a symbol of wealth.
Q 05Which sharp-toothed South American river fish has a plant-eating relative, the pacu, with squarer, straighter teeth?
Piranha
Piranha have razor-sharp teeth set in a pronounced underbite, while the pacu's are built for a diet of plants. The pacu is also the bigger fish by far, growing to more than a metre long.
Q 06Which pet fish, often dumped in ponds after outgrowing its tank, is an invasive pest in North America and Australia?
Goldfish
Goldfish released into the wild typically reach 12 to 22 cm, far bigger than most bowls allow. One caught in an English pond in 2010 measured 41 cm and weighed 2.3 kg.
Q 07Mexico's famous cave fish, descended from ordinary river fish, has lost which body parts over many generations?
Its eyes
Its eyes have gone entirely, leaving empty sockets covered with skin. The fish steers instead with extra-sensitive organs along its body that pick up slight changes in water pressure.
Q 08Salmon returning from the ocean are thought to find the very stream where they hatched mainly by using which sense?
Smell
Smell leads salmon to the entrance of their home river and on to the gravel where they hatched, because each stream has its own scent. Out at sea they are thought to steer by magnetism instead.
Q 09When two kissing gouramis press their lips together in an aquarium, what are the fish thought to be doing?
Fighting
Fighting is the usual reading: the 'kiss' is treated as ritualized aggression, a way for rivals to challenge each other. The same toothed lips are used to rasp algae off stones.
Q 10A 300 kg specimen of which fish, caught in the Mekong in 2022, is the largest strictly freshwater fish ever documented?
Stingray
Stingray is the answer: the giant freshwater stingray pulled from the river measured 3.98 metres long and 2.2 metres across. The species is endangered, with numbers down by up to half in Thailand and Cambodia.
Q 11Largemouth and smallmouth bass, the black basses prized by North American anglers, belong to which fish family?
Sunfish
Sunfish is the family, the same one as the little bluegill that largemouths eat. The largemouth is the biggest of the black basses, with a top recorded length of 75 cm.
Q 12The Jack Dempsey, an aquarium cichlid known for its aggression, is named after a 1920s champion in which sport?
Boxing
Boxing gave the fish its name: its aggressive nature and strong facial features were likened to the heavyweight champion. Both parents turn fiercely protective once there are eggs to defend.
Q 13Which widely farmed fish, raised in ponds since Ancient Egypt, is sometimes sold as 'St Peter's fish'?
Tilapia
Q 21Which long-lived, scaleless fish is armoured instead with five rows of bony plates called scutes?
Sturgeon
Sturgeon fossils go back to the Late Cretaceous, when dinosaurs were still around. The adults have no teeth, so a feeding fish extends its lips and vacuums up soft food whole.
Q 22Which livebearing aquarium fish, named for a man who sent specimens from Trinidad, is also called the millionfish?
Guppy
Guppy honours Robert John Lechmere Guppy, who sent the fish to London's Natural History Museum. It now lives on every continent except Antarctica, mostly after being released to eat mosquito larvae.
Q 23Which tiny South American aquarium fish has an iridescent blue stripe that fades to grey or black as it rests at night?
Neon tetra
Tilapia live in the Sea of Galilee, where the Gospel of Matthew has the apostle Peter catch a fish carrying a coin. The gospel never says what kind of fish it was.
Q 14Which African lake holds more fish species than any other lake on Earth, including at least 700 kinds of cichlid?
Malawi
Malawi cichlids can have tiny ranges, with some restricted to stretches of rocky coastline only a few hundred metres long. The IUCN lists 117 of the lake's cichlids as threatened.
Q 15Which huge predator, released into Lake Victoria in the 1950s, is blamed for wiping out hundreds of native fish species?
Nile perch
Nile perch can reach nearly 2 metres and 200 kg, and several hundred native species went extinct or close to it after its release. It is still traded under the misleading name Victoria perch.
Q 16Which jawless parasite spread through the Great Lakes, probably via shipping canals, and attacked the native lake trout?
Sea lamprey
Sea lamprey clamp onto other fish with a round, toothed sucker, and each can kill about 40 pounds of fish in a feeding period of 12 to 18 months. The Erie and Welland canals are the likely way in.
Q 17Which Asian predator, now invasive in several US states, can breathe air and survive out of water for several days?
Snakehead
Snakehead gulp air using a special organ above the gills, and the young may even wriggle short distances overland. In its native Asia it is a valued food fish, which is how it came to be shipped abroad.
Q 18Many cichlids of Africa's great lakes protect their eggs and newly hatched young by carrying them where?
In their mouths
In their mouths, usually the mother's, the brood is held safe for long periods. In many species the male fertilises the eggs only after the female has already scooped them up.
Q 19What name is given to the chain of low pools that lets migrating salmon and trout get past a dam?
Fish ladder
Fish ladder steps are low weirs with a resting pool between each one, so fish can climb in stages. Rough versions made from bundles of branches were in use in 17th-century France.
Q 20Which Robert Redford film follows two Montana brothers who learn fly fishing for trout from their minister father?
A River Runs Through It
A River Runs Through It stars Brad Pitt and Craig Sheffer as the Maclean brothers and is based on Norman Maclean's novella about his own family. It won the Oscar for Best Cinematography.
Neon tetra colours come from guanine crystals in the skin that respond to the light. Most of those sold in the United States are farm-raised in Southeast Asia, far from their home streams.
Q 24Water constantly diffuses into the bodies of freshwater fish, which shed the excess by producing plenty of what?
Dilute urine
Dilute urine carries the surplus water out, while the gills actively pull salt back in. A sea fish has the opposite problem: it tends to lose water and gain salt.
Q 25Bettas and gouramis can gulp air at the surface thanks to which folded breathing structure above the gills?
Labyrinth organ
Labyrinth organ tissue takes oxygen straight from the air. That lets a betta thrive in rice paddies, ditches and large puddles, where the water holds too little oxygen for most other fish.
Q 26The floating nest that a male betta builds at the surface to hold his eggs is made of what?
Bubbles
Bubbles blown with an oral secretion make up the raft, which the male then guards. Most fish that build these nests live in warm, standing water that is short of oxygen.
Q 27Despite its name, South America's electric eel is not a true eel but belongs to which order of fish?
Knifefish
Knifefish are South American fish that sense electricity, and the electric eel is the order's heavyweight, with shocks of up to 860 volts. It also has to come up regularly to breathe air.
Q 28Which Central American lake has sharks that were once thought to be a species of their own, trapped in fresh water?
Nicaragua
Nicaragua's lake sharks are ordinary bull sharks that travel the rapids of the San Juan River, almost like salmon. Tagged ones have reached the open ocean in as little as seven days.
Q 29Which composer's 'Trout' Quintet takes its nickname from a movement based on his own earlier song about the fish?
Franz Schubert
Franz Schubert wrote the quintet at 22 and built its fourth movement as variations on his song Die Forelle. It swaps the usual second violin for a double bass, and was published only after his death.
Q 30George Perry's 1932 world-record largemouth bass was tied in 2009 by a fish from Lake Biwa in which country?
Japan
Japan's fish, landed by Manabu Kurita, was actually an ounce heavier than Perry's. The record is shared because a new one has to beat the old by at least two ounces.