Shark facts
Short facts, and straight answers to things people say about sharks. Every one lists where we found it.
Short facts, and straight answers to things people say about sharks. Every one lists where we found it.
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Most sharks have five gill slits on each side of the head, and they take oxygen from the water passing over their gills. Bottom-dwellers such as wobbegongs and angelsharks also have openings behind the eyes, called spiracles, to draw water in.
Sources: Sharks4Kids: Shark gills, Wikipedia: Shark
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A great white is grey-black on top and pale to white underneath, with a sudden colour change along its sides. Scientists call this countershading. It helps the shark blend in when seen from above or from below.
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The velvet belly lanternshark makes its own light, and researchers found that hormones, not nerves, control it. Melatonin gives a slow glow that lasts for hours, and another hormone, alpha-MSH, turns it off. The glow may help the shark hide or signal, though that is still a guess.
Sources: Science News: Hormones give lantern sharks the glow
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Sharks have no swim bladder, so they would sink. Instead they have big livers full of oil, which is lighter than seawater, and a light skeleton of cartilage to help them stay afloat.
Sources: Natural History Museum: Do sharks have bones?, Hawaii DLNR: Skeleton and buoyancy
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Instead of ordinary scales, sharks have tiny tooth-like scales called dermal denticles. A lab study found that scales with tiny ridges can cut drag by about 2 percent compared with a flat surface.
Sources: University of Leeds and Hull study (White Rose), Wikipedia: Shark anatomy
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A shark can shed many thousands of teeth in its lifetime. New ones grow in rows behind the old ones, and how fast they are replaced depends on the shark, from every week or two to every few months.
Sources: Florida Museum: Shark teeth, Wikipedia: Shark
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A thresher shark's tail is nearly half as long as its whole body. Scientists filmed thresher sharks slapping schools of sardines with it, stunning or hurting the fish before eating them.
Sources: Bangor University: thresher sharks use tail slaps to hunt, NBC News: Thresher shark stuns prey
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Most sharks are about as warm as the water around them, but the shortfin mako keeps its swimming muscles warmer. A 2025 study found them to be on average about 1.5 to 3.9 degrees Celsius warmer than the sea.
Sources: Journal of Animal Ecology (2025), via PubMed Central, University of St Andrews: Secret of the great white shark revealed
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A whale shark has 20 filtering pads, 10 on each side, inside its huge mouth, and its gill slits act as filter screens. The screens keep food about 2 to 3 millimetres across or larger, and the shark often feeds head-up near the surface.
Sources: Florida Museum: Whale shark profile
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The pale spots on a whale shark's back are unique, a bit like a fingerprint. Scientists adapted star-mapping software from astronomy to match photos and recognise individual sharks.
Sources: ScienceDaily: Why a whale shark's spots could help save its skin