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Is this animal a marine mammal or a fish?

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The answers

Marine mammal or fish?

Marine mammal 12

  • Humpback whale Right Wrong

    Like all cetaceans, it breathes air through its blowholes and suckles its young. The males are famous for their complex songs, which can last for hours, and the species for its spectacular leaps out of the water.

  • Bottlenose dolphin Right Wrong

    This cetacean breathes through a blowhole on top of its head. To sleep without drowning, it keeps one half of its brain awake, which allows it to keep surfacing to breathe.

  • Orca Right Wrong

    Despite its nickname of "killer whale", the orca is the largest member of the dolphin family. This mammal lives in close-knit family pods, led by the oldest females.

  • Sperm whale Right Wrong

    The largest toothed predator on the planet, this cetacean holds its breath for over an hour to dive more than 1,000 metres down and hunt squid. Photo: a mother and her calf.

  • Narwhal Right Wrong

    Nicknamed the "unicorn of the sea", this Arctic cetacean carries a long spiral tusk that is actually a tooth. It can grow to more than two metres long.

  • Beluga Right Wrong

    This white whale of the Arctic is nicknamed the "canary of the sea" for the variety of its whistles. Unlike most cetaceans, it can turn its head, as the vertebrae of its neck are not fused together.

  • Harbour seal Right Wrong

    This pinniped has no visible external ears and moves on land by wriggling on its belly. Like all marine mammals, it breathes air and the female suckles her pup.

  • California sea lion Right Wrong

    You can tell it from a seal by its small visible ears and its rear flippers, which it tucks under its body to walk on land. It is a very playful mammal.

  • Walrus Right Wrong

    Its long tusks, which are canine teeth, help it haul itself onto the ice. This Arctic mammal finds shellfish and worms on the seabed thanks to its hundreds of sensitive whiskers.

  • Manatee Right Wrong

    Nicknamed the "sea cow", this herbivorous mammal grazes on aquatic plants and surfaces to breathe every few minutes. It is a distant cousin of the elephant. Photo: a mother and her calf.

  • Dugong Right Wrong

    A cousin of the manatee, this mammal grazes on the seagrass meadows of the Indian and Pacific Oceans. You can recognise it by its crescent-shaped tail, similar to a dolphin's.

  • Sea otter Right Wrong

    This marine mammal has no layer of blubber: it keeps out the cold thanks to the densest fur in the animal kingdom. It cracks shellfish open on its belly using stones.

Fish 12

  • Bluefin tuna Right Wrong

    This bony fish breathes through its gills. It can exceed 3 metres and 600 kilos, and is one of the rare fish able to keep its body warmer than the surrounding water.

  • Great white shark Right Wrong

    Sharks are fish whose skeleton is made of cartilage rather than bone. The great white breathes through its gills, visible as slits on the sides of its head.

  • Whale shark Right Wrong

    Despite its name, it really is a shark, and therefore a fish: the largest in the world, which can exceed 12 metres. This gentle giant feeds on plankton, which it filters through its gills.

  • Clownfish Right Wrong

    This little fish lives sheltered among sea anemones, protected from their stinging tentacles by a layer of mucus. All are born male: when the female dies, the largest male in the group changes sex.

  • Manta ray Right Wrong

    A cousin of the sharks, the manta ray is a cartilaginous fish. Its wingspan can reach 7 metres and it has one of the largest brains, relative to its size, of any fish.

  • Seahorse Right Wrong

    Despite looking like a little horse, the seahorse is a bony fish that breathes through gills. Its special feature: it is the male that carries the eggs in a pouch on its belly until they hatch.

  • Swordfish Right Wrong

    This fish uses its long sword-shaped bill to stun its prey. It can warm its eyes and brain to hunt in the cold waters of the deep. Photo: a mounted specimen.

  • Ocean sunfish Right Wrong

    Also known as the mola, it is the heaviest bony fish: it can weigh more than two tonnes. The female lays hundreds of millions of eggs at a time, a record among vertebrates.

  • Grouper Right Wrong

    This large fish of rocky seabeds is born female and becomes male as it ages. Long a victim of spearfishing, it is now protected along the French Mediterranean coast.

  • Barracuda Right Wrong

    This predatory fish with a long body and razor-sharp teeth hunts by ambush, surprising its prey with sudden bursts of speed. The young often move around in schools.

  • Moray eel Right Wrong

    Despite its snake-like body, the moray is a fish. If it keeps opening and closing its mouth, it isn't a threat: it is pumping water over its gills in order to breathe.

  • Atlantic salmon Right Wrong

    This fish is born in a river, goes out to sea to grow, then returns to spawn in the river where it was born, swimming upstream and sometimes up waterfalls.

They all live in the water, often have a streamlined body and fins, and yet they belong to completely different branches of the tree of life. Marine mammals breathe air with lungs and suckle their young, while fish breathe underwater through their gills. Some names are misleading, and so are some silhouettes: a grey back cutting through the waves could be either. It's up to you to sort them out before the timer runs out!

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12 cards, 24 seconds: the timer starts with your first choice.

Frequently asked questions

How do you tell a marine mammal from a fish?

Marine mammals breathe air with lungs and have to come up to the surface. They are warm-blooded, and the females suckle their young. Fish, on the other hand, breathe the oxygen dissolved in water through their gills and, for the most part, lay eggs.

Where do marine mammals come from?

Their ancestors lived on dry land. Several groups of mammals returned to the sea tens of millions of years ago. Today there are just over 130 species of marine mammals.

Why do they look so alike?

This is what's known as convergent evolution: very distantly related species, facing the same constraints, end up developing similar shapes. To swim fast, a streamlined body and fins are an advantage, whether you're a fish or a mammal.

What about sea turtles, penguins and jellyfish?

Neither! Sea turtles are reptiles, penguins are birds and jellyfish are cnidarians, with no skeleton and no brain. This quiz only includes animals that genuinely belong to one of the two categories: marine mammal or fish.

Photo credits

Humpback whale : Giles Laurent, CC BY-SA 4.0, via Wikimedia Commons ; Bottlenose dolphin : Giles Laurent, CC BY-SA 4.0, via Wikimedia Commons ; Orca : H. Zell, CC BY-SA 3.0, via Wikimedia Commons ; Sperm whale : Gabriel Barathieu, CC BY-SA 2.0, via Wikimedia Commons ; Narwhal : Gazprom Neft, CC BY-SA 4.0, via Wikimedia Commons ; Beluga : Brian Gratwicke, CC BY 2.0, via Wikimedia Commons ; Harbour seal : Charles J. Sharp, CC BY-SA 4.0, via Wikimedia Commons ; California sea lion : Rhododendrites, CC BY-SA 4.0, via Wikimedia Commons ; Walrus : Megapixie, domaine public, via Wikimedia Commons ; Manatee : Galen Rathbun, domaine public, via Wikimedia Commons ; Dugong : Julien Willem, CC BY-SA 3.0, via Wikimedia Commons ; Sea otter : Mike Baird, CC BY 2.0, via Wikimedia Commons ; Bluefin tuna : Auteur inconnu, domaine public, via Wikimedia Commons ; Great white shark : Elias Levy, CC BY 2.0, via Wikimedia Commons ; Whale shark : Arturo de Frias Marques, CC BY-SA 4.0, via Wikimedia Commons ; Clownfish : Nick Hobgood, CC BY-SA 3.0, via Wikimedia Commons ; Manta ray : Arturo de Frias Marques, CC BY-SA 4.0, via Wikimedia Commons ; Seahorse : Hans Hillewaert, CC BY-SA 4.0, via Wikimedia Commons ; Swordfish : Citron, CC BY-SA 3.0, via Wikimedia Commons ; Ocean sunfish : Per-Ola Norman, domaine public, via Wikimedia Commons ; Grouper : Diego Delso, CC BY-SA 4.0, via Wikimedia Commons ; Barracuda : Diego Delso, CC BY-SA 4.0, via Wikimedia Commons ; Moray eel : Diego Delso, CC BY-SA 4.0, via Wikimedia Commons ; Atlantic salmon : Hans-Petter Fjeld, CC BY-SA 2.5, via Wikimedia Commons