Only three sharks are filter feeders — the whale shark, the basking shark and the megamouth shark — and two of them are the largest fish alive.
They do not do it the same way. A whale shark actively sucks water in or rams it through twenty filter pads. A basking shark simply swims with its mouth open and lets roughly 1,500 to 2,000 cubic metres of water an hour pass across its gill rakers. The megamouth, hauled up for the first time in 1976 and still known from fewer than three hundred encounters, follows plankton up and down the water column every night.
- Filter-feeding sharks3 of more than 500 species
- Reliable maximum, basking sharkAbout 10 m (33 ft)
- Megamouth records since 1976Fewer than 300 worldwide
On this page
How a shark lives on plankton
Filter feeding is a volume problem. Plankton is nutritious but thinly spread, so an animal that wants to live on it has to process water by the tonne and sort the contents out fast enough to stay ahead of the effort. Whales solved this with baleen. The three sharks that took the same route solved it inside the gill arches instead, using structures that sit in the path of the water already flowing across the gills for respiration.
That is the neat part of the design: the same current that carries oxygen also carries dinner, and the machinery for both sits in one place. In the basking shark the sorting is done by long, bristle-like gill rakers; in the whale shark it is done by twenty filter pads, ten on each side, which work more like a sieve mat than a comb; the megamouth has papillose gill rakers of its own design. None of the three uses its teeth. All three have them, in the hundreds or thousands, and none of them matters.
What follows is what each species is actually measured at, rather than what gets repeated. The numbers in circulation for these sharks are among the worst on the internet, because very large animals are almost never weighed and rarely measured properly.
The whale shark
Rhincodon typus is the largest fish alive, and the largest individual that has actually been measured was 12.65 m. Longer animals are reported constantly — eighteen metres, twenty metres — but those figures come from estimates made alongside a moving shark, not from a tape. Published weights are worse: nearly all of them are calculated from length, so a headline mass of twenty tonnes is arithmetic rather than a weighing.
The head is wide and blunt, the mouth sits at the front rather than underneath as it does in most sharks, and the body carries a grid of pale spots and stripes that is unique to each animal and used to identify individuals across years. There are five gill slits a side, two dorsal fins, and a pair of small spiracles behind the eyes — openings left over from an ancestral gill slit, not gill slits themselves, as the old version of this page had it.
Feeding is active, which sets the whale shark apart from the other two. It either rams, swimming forward with the mouth open, or suctions, hanging near-vertical in a dense patch of eggs or krill and gulping. It works warm surface water above about 21°C but is not confined to it: tagged animals have been recorded diving past 1,900 metres. Whether it is safe to swim beside one is covered in are whale sharks dangerous.
The basking shark
Cetorhinus maximus is the second-largest fish in the sea and the one most often underestimated. Typical adults run seven to nine metres, and the ceiling the literature will defend is around 10 metres. A 12.27 m fish netted off Musselburgh in Scotland in 1851 is still printed as the record, but nothing survives that would let anyone check how it was measured. Its gill slits are the giveaway in the field: they run so far around the head that they nearly meet, which no other large shark does, and which is nothing like the great white it is so often mistaken for at a distance.
It feeds passively. The shark swims at roughly one metre per second with its mouth open and its gill rakers raised, and water simply passes through — somewhere around 1,500 to 2,000 cubic metres in an hour, which is a weight of water measured in thousands of tonnes. It prefers water between about 8 and 14°C and works surface fronts and river mouths where zooplankton concentrates.
One long-standing claim about the species has been overturned. Basking sharks were said to shed their gill rakers and hibernate on the seabed through winter, because they vanished from the surface. Satellite tagging showed the opposite: they stay active all year, move to deeper water and continue feeding, with tracked animals recorded past 1,000 metres and crossing whole ocean basins.
The megamouth shark
Megachasma pelagios is the newest large animal on the list of things science knows about. The first one was hauled up on 15 November 1976 by a United States Navy vessel off Oahu, Hawaii, tangled in a parachute sea anchor at around 165 metres, and it turned out to need a new family and a new genus of its own. The old version of this page put the running total at 55 records; that number is long out of date, and the confirmed tally now runs into the hundreds — still fewer than three hundred animals in total — with a large share of the recent ones coming from fisheries in the western Pacific.
It is the smallest of the three and still substantial: scientifically measured specimens top out at about 5.5 metres, with females running larger than males. The six- and seven-metre animals that turn up in news and fishery reports have never been backed by a published measurement. The body is soft and heavy-set, the head is enormous in proportion, and the mouth is lined with roughly fifty rows of small teeth that do no work.
A single tracked megamouth showed a clean daily rhythm, sitting between about 120 and 165 metres in daylight and rising to 12 to 25 metres after dark, following the vertical migration of the plankton it eats. One claim worth dropping is the glowing mouth: the pale band along its upper jaw is widely described as a row of bioluminescent organs, but no light-producing tissue has ever been confirmed, and reflection is the likelier explanation.
What the three have in common, and what they do not
They converged on the same diet from three different starting points. The whale shark is a carpet shark, related to wobbegongs and nurse sharks; the basking shark and the megamouth are mackerel sharks, in the same order as the great white and the makos. Filter feeding evolved separately in each lineage, which is why the sorting hardware differs so much between them.
What they do share is a set of consequences. All three are slow to mature and produce few young, which makes them poor at recovering from being fished, and all three carry large, valuable fins. The basking shark was hunted commercially for liver oil into the twentieth century and its populations have still not returned in several of its old strongholds. The whale shark is listed as Endangered; the basking shark is in the same position across much of its range. The wider account is in why sharks are endangered.
They also share a clean incident record. None of the three can bite anything larger than a small fish, and they sit at the top of our list of the least dangerous sharks for that reason. If you want the mechanics of how the same gill arches handle oxygen and food at once, how sharks breathe covers the respiratory half of the job.
Frequently asked questions
Which sharks are filter feeders?
Three species: the whale shark, the basking shark and the megamouth shark. Every other described shark hunts prey it can bite. The three are not close relatives either — the whale shark is a carpet shark, while the basking shark and megamouth are mackerel sharks, so filter feeding evolved separately in each line.
What is the largest filter-feeding shark?
The whale shark, and it is the largest fish in the sea by a wide margin. The longest individual genuinely measured was 12.65 metres. Longer figures are common in print but come from estimates made beside a swimming animal, and published weights are almost always calculated from length rather than taken on a scale.
How much water does a basking shark filter?
Roughly 1,500 to 2,000 cubic metres an hour, which is a weight of water in the thousands of tonnes. It does this passively, swimming at around one metre per second with the mouth open and the gill rakers raised, so the only energy cost is the swimming it would be doing anyway.
Do basking sharks hibernate in winter?
No. They were believed to shed their gill rakers and lie dormant on the seabed because they disappeared from the surface each winter. Satellite tagging disproved it: the sharks stay active year round, move into deeper water, keep feeding, and some cross entire ocean basins between seasons.
How rare is the megamouth shark?
Rare enough that it was unknown until a US Navy vessel hauled one up off Hawaii in November 1976. The confirmed tally now runs into the hundreds, though still fewer than three hundred animals worldwide, many of them from western Pacific fisheries, so it is far better documented than the figure of 55 that still circulates online.
Does the megamouth shark glow?
Probably not. The pale band running along its upper jaw is often described as a row of light-producing organs used to lure plankton, but no bioluminescent tissue has ever been confirmed in the species. The likelier explanation is that the band simply reflects whatever light reaches that depth.
Do filter-feeding sharks have teeth?
All three do, and none of them uses them. A whale shark carries around three hundred rows of teeth about six millimetres long, and the megamouth has roughly fifty rows of small ones. They are inherited from ancestors with different diets. Food is sorted by filter pads or gill rakers instead.
Are filter-feeding sharks dangerous to people?
No. None of the three can take anything larger than a small fish, and our incident database holds no injury caused by any of them. The only genuine hazards are mechanical: a tail stroke from a very large animal, or a boat and a swimmer working the same patch of surface water.
References
A small team focused on researching sharks and making marine biology easy to understand. Every page is reviewed against current species records and the SharkSider attack database, and updated when new incidents or research appear.
Published June 6, 2016 · Last updated September 23, 2026 · Filed under Cool Shark Facts.
