50 Fun Facts About Cartilaginous Fish

A cartilaginous fish has a skeleton made of the same bendy tissue as which parts of the human body?

Ears and nose tips are shaped by cartilage, the gristly tissue that forms a shark's whole skeleton. It is far lighter than bone, which helps these fish stay buoyant.

Fossils show sharks were already swimming the seas before which of these first appeared on Earth?

Trees came later: sharks appear in the fossil record around 450 million years ago. They have since survived five mass extinctions, including the one that ended the dinosaurs.

Which slow-swimming deep-water species, thought to live for centuries, is the longest-lived vertebrate known?

The Greenland shark may live for 272 years or more, longer than any other animal with a backbone. Scientists worked out the ages by radiocarbon dating the cores of the sharks' eye lenses.

Shark skin, covered in tiny tooth-like scales, feels just like which workshop material?

Sandpaper is the usual comparison, because the scales, known as dermal denticles, are built like miniature teeth. They all point toward the tail, which cuts friction with the water as the animal swims.

Which gentle, spotted giant that feeds mostly on plankton is the largest fish alive today?

The whale shark can exceed 12 metres in length, and each one's pattern of spots is as unique as a fingerprint. It even appears on the back of the Philippine 100-peso note.

Which extinct giant shark, among the largest predators that ever lived, is known mainly from its fossil teeth?

Megalodon means 'big tooth' in Greek. It was a giant mackerel shark that died out about 3.6 million years ago, and its cartilage skeleton rarely fossilised, so teeth are most of what remains.

A popular book wrongly claimed sharks never get which disease, launching a trade in cartilage pills?

Cancer does strike sharks: researchers have recorded tumours in at least 18 species. Clinical trials of the supplements have found no benefit for patients.

Jelly-filled pores called ampullae of Lorenzini let sharks and rays detect what from prey hidden in sand?

Electric fields are given off by every living animal, and sharks sense them more keenly than any other creature. The same organs may help them navigate using Earth's magnetic field.

Whether it hatches from an egg case or is born live, a baby shark is known by which name?

Pup is the term, shared with young seals and dogs. Newborn sharks arrive fully formed and get no parental care, so they must fend for themselves at once.

Which species terrorised Amity Island as the monster in Steven Spielberg's 1975 film Jaws?

A great white shark was the villain, played by mechanical models that broke down so often that Spielberg mostly hinted at the monster instead. The crew nicknamed the props Bruce.

Which sharks have a wide, flattened head called a cephalofoil that sharpens their depth perception?

Hammerheads gain better binocular vision from their wide-set eyes. They also use the broad head as a tool, pinning rays to the seabed before eating them.

Which giant ray takes its name from a Spanish and Portuguese word for a cloak or blanket?

The manta ray has the largest brain of any fish. Its name recalls the blanket-shaped traps that fishermen traditionally used to catch rays.

Beachcombers often find the leathery egg cases of skates and small sharks, which go by which folk name?

A mermaid's purse is woven from strands of collagen and can protect a growing embryo for anything from a few months to more than a year. Many have tendrils that anchor them to the seabed.

Which wildlife presenter died in 2006 when a stingray's barb pierced his chest on the Great Barrier Reef?

Steve Irwin, television's Crocodile Hunter, was filming an underwater documentary at Batt Reef. His death is believed to be the only fatal stingray strike ever captured on video.

With no gas-filled swim bladder, sharks stay buoyant thanks to an enormous, oil-rich version of which organ?

The liver of a shark can make up as much as 30% of its total body mass. Even so, the lift is limited, so sharks also use their fins like wings to hold their depth.

Some open-ocean sharks must keep swimming forward their whole lives in order to do what?

To breathe, these sharks must drive oxygen-rich water in through the open mouth, and they would suffocate if held still. Bottom-dwellers such as nurse sharks can take in water while resting.

Most sharks have five to seven of which exposed openings on each side of the head, with no bony cover?

Gill slits stay uncovered in sharks, while bony fish tuck theirs beneath a hard flap. Rays carry the same openings on the underside of their flattened bodies.

Which naval weapon is named after a genus of rays that stun their prey with a powerful jolt?

The torpedo borrows its name from the rays, whose own name comes from a Latin word for sluggishness. A Roman physician recorded using the live fish to treat headaches and gout.

Which critically endangered family of giant rays carries a long, flat snout lined with teeth on both sides?

Sawfish swipe the toothed snout sideways to incapacitate passing prey, and can sense a hidden meal from about 40 centimetres away. All five species are critically endangered.

Hákarl, a pungent national dish of fermented shark meat hung to dry for months, comes from which country?

Iceland's hákarl has to be cured because the fresh meat is poisonous, loaded with urea. The process leaves so much ammonia that first-time tasters often gag.

Which small species gouges round plugs of flesh from dolphins and tuna, and has even damaged submarines?

The cookiecutter shark is named for its bite marks, which look as if they were stamped out with a baking tool. Also called the cigar shark, it grows only about half a metre long.

Which coastal predator has swum 700 miles up the Mississippi River to Illinois and also lives in Lake Nicaragua?

The bull shark can thrive in both salt and fresh water, a rare talent among its relatives. In Africa the same species is known as the Zambezi shark, after the river.

Which species has a scythe-like tail as long as its body, used as a whip to stun schools of fish?

The thresher shark is named for that long, thresher-like tail. The best-known species has a second name too: the fox shark, echoing the Greek word for fox in its scientific name, Alopias.

Which pink-skinned deep-sea species, often called a living fossil, snatches prey by shooting its jaws forward?

The goblin shark is the last survivor of a family about 125 million years old. Its jaws can spring out almost to the tip of its long, flat snout.

Which deep-water relatives of sharks are known informally as ghost sharks, ratfish and spookfish?

Chimaeras crush their food with beak-like tooth plates instead of rows of sharp teeth. Those plates, likened to a rodent's incisors, earned them one more nickname: rabbit fish.

Which fish clamps onto sharks, rays and turtles with a sucker on top of its head, hitching a ride?

The remora's sucker is a reshaped dorsal fin lined with slats that grip by suction. In return for the lift, it picks parasites and loose skin off its host.

The ridged texture of shark skin inspired which piece of Olympic kit, first worn at the Sydney Games in 2000?

Swimsuits in Speedo's Fastskin range copied the bumps and ridges of sharkskin to slip through the water. Later research suggested the pattern does little for humans, who move differently.

Renaissance Europeans believed fossil shark teeth found in rocks were the petrified what of dragons and snakes?

Tongues was the answer of the day, hence the old name tongue stones. Nobles wore the fossils as pendants, trusting them to cure snake bites and neutralise poison.

Which sense organ, a row of pores along each flank, lets sharks and other fish feel vibrations in the water?

The lateral line picks up movement and vibration in the surrounding water. It lets a predator turn toward struggling prey before the target comes into view.

Which slow-moving plankton eater, the second-largest fish alive, cruises the surface with its huge mouth wide open?

The basking shark gets its name because it seems to be sunbathing as it feeds in the warmer water at the surface. For all its bulk, it is a harmless filter feeder.

Which rare plankton-eating species was unknown to science until one tangled in a US Navy ship's anchor off Hawaii?

The megamouth shark turned up in 1976, and its discovery ranks beside the coelacanth as one of the most sensational fish finds of the twentieth century.

Which open-ocean species is the fastest of all sharks, reaching 46 mph in short bursts?

The shortfin mako can hit 74 km/h in short sprints. In Māori, the word mako means either the animal itself or one of its teeth, which were highly prized.

Which small reef species 'walks' across the seabed on paddle-like fins and can survive two hours without oxygen?

The epaulette shark lives in tidal pools that run short of oxygen at night. It copes by boosting blood flow to its brain and switching off the functions it can do without.

Which well-camouflaged fish of Australian reefs has a name thought to mean 'shaggy beard' in an Aboriginal language?

The wobbegong, a flat carpet shark, is named for the weed-like lobes that fringe its jaw. They help to disguise the animal and also work as sensory barbs.

Which species, able to gulp air to hover motionless, has embryos that devour their smaller siblings in the womb?

The sand tiger shark starts a pregnancy with dozens of embryos, but the largest in each womb eats the rest, so only two are born. Biologists call it adelphophagy, meaning eating one's brother.

Female sharks kept apart from males have still produced young through which form of virgin birth?

Parthenogenesis was confirmed by genetic fingerprinting, which showed the offspring carried no DNA from a father and ruled out the idea that the mothers had stored sperm.

Australian fish and chip shops commonly sell boneless shark meat under which trade name?

Flake usually means gummy shark. It became the most common fish in Australian chip shops thanks to a ready supply, a low price and the lack of bones to pick out.

River stingrays of the genus Potamotrygon, which live in fresh water, are native to the rivers of which region?

South America's river stingrays live in waters draining to the Caribbean and the Atlantic. A fossil from Peru shows the family has been there since the Eocene epoch.

According to a 2021 study, which human activity is driving more than a third of sharks and rays toward extinction?

Overfishing has cut the number of oceanic sharks and rays by about 71% in 50 years. These fish breed slowly, raising only a few well-developed young at a time.

Which scientific class, named from the Greek for 'cartilage fish', unites the sharks, rays and skates?

Chondrichthyes is divided into two subclasses: one holds the sharks, rays and skates, the other the deep-water ghost sharks. The name joins the Greek words khondros and ikhthys.

Turning a shark upside down sends it into which trance-like state, used by scientists to handle the animals?

Tonic immobility steadies and relaxes the animal's muscles. Some biologists link the reflex to mating, when a bite from the male can hold a female still.

Which openings just behind the eyes let a ray lying on the seabed draw in water without using its mouth?

Spiracles sit on top of the head, so a ray half-buried in sand can still take in clean water. Fast open-ocean sharks have only tiny ones, or none at all.

Which prehistoric cartilaginous fish, named 'spiral saw', carried a buzzsaw-like whorl of teeth in its lower jaw?

Helicoprion is known almost entirely from those spiral whorls, which make up nearly every fossil of it ever found. It probably used them to grasp and slice soft-bodied prey such as ancient squid relatives.

Which eel-like deep-sea species swallows prey whole with flexible jaws holding 300 needle-like, backward-curving teeth?

The frilled shark is named for the fringed look of its throat. It hunts like a snake, curling its tail against a rock and then lunging at squid and smaller fish.

The bonnethead, the first shark found to be an omnivore, eats and digests large amounts of which plant?

Seagrass makes up about 62% of what a bonnethead has in its gut. Lab tests showed the animal digests roughly half of it, helped by enzymes that break down plant fibre.

Which Pacific species defends itself by swallowing water until it balloons to about twice its normal size?

The swell shark bends into a U, grips its own tail fin in its mouth and sucks in water. Its scientific name, ventriosum, refers to the same trick.

A 300-kilogram stingray that set the record for the largest freshwater fish in 2022 was caught in which river?

The Mekong giant measured nearly four metres from snout to tail tip. Sturgeon can grow heavier, but they divide their lives between rivers and the sea.

Open-water sharks are dark on top and pale underneath, a camouflage colour scheme known by which name?

Countershading hides a shark twice over: seen from below, the pale belly blends with the bright surface, and seen from above, the dark back melts into the deep.

Scientists estimate the age of most sharks by counting pairs of growth bands in which part of the skeleton?

Vertebrae lay down light and dark bands as a shark grows. One pair does not always equal one year, so researchers have to check the rate for each species.

Which author regretted the fear of sharks spread by his 1974 bestseller and became a campaigner for marine conservation?

Peter Benchley wrote the novel Jaws, a bestseller for 44 weeks, and co-wrote the script of the film. He later said the story had fed false beliefs about the animals.