The Japanese bullhead shark (Heterodontus japonicus) is a small, slow bullhead shark of the north-western Pacific that reaches about 1.2 m (3.9 ft) and lives on rocky and kelp-covered bottoms between roughly 6 and 37 m. It is sandy brown with eleven to fourteen darker bands, has a blunt pig-like snout, a spine in front of each dorsal fin and jaws that carry gripping teeth at the front and crushing plates at the back.
It feeds at night on sea urchins, shellfish, crabs and small fish. Females lay six to twelve spiral-flanged egg cases in shared rock nests, and the eggs take about a year to hatch at roughly 18 cm. Its Red List category is Least Concern. It has never been implicated in an attack on a person and is harmless unless picked up.
- Maximum length1.2 m (3.9 ft); most adults 80–100 cm
- WeightNo published maximum; a few kilograms
- LifespanNot reliably recorded
- Depth range6–37 m (20–121 ft)
- DietSea urchins, molluscs, crustaceans, small fish
- IUCN statusLeast Concern
- Kingdom
- Animalia
- Phylum
- Chordata
- Class
- Chondrichthyes
- Order
- Heterodontiformes
- Family
- Heterodontidae
- Genus
- Heterodontus
- Species
- Heterodontus japonicus
- Family (common)
- Bullhead sharks
- Also known as
- Japanese horn shark, Nekozame (Japan)
On this page
- How to recognise a Japanese bullhead shark
- How big does the Japanese bullhead shark get?
- Where Japanese bullhead sharks live
- What Japanese bullhead sharks eat
- Behaviour, senses and defences
- Eggs, nests and lifespan
- Is the Japanese bullhead shark dangerous?
- Conservation status and threats
- Close relatives and look-alikes
- Frequently asked questions
- References
How to recognise a Japanese bullhead shark
A Japanese bullhead shark looks less like a shark than like a small, blunt-headed reef fish that has been handed fins and a tail. The body is cylindrical and stiff, the head short and squared off, and the snout ends in a rounded, almost porcine muzzle with the nostrils joined to the mouth by deep grooves. Low ridges run above each eye, far lower and softer than the tall crests of the crested bullhead shark.
Colour is the fastest field mark. The ground colour is a pale sandy brown crossed by eleven to fourteen broad, darker brown bands that run down the flanks and fade with age, so adults look washed out beside the boldly marked young. There are no spots, which separates it immediately from the spotted horn shark of California, and the bands are wide and soft-edged rather than the narrow ruled stripes of the zebra bullhead shark, which shares the same seas.
Two further features settle the identification. Each of the two dorsal fins is preceded by a stout spine, the first dorsal starting over the bases of the broad, paddle-shaped pectoral fins, and an anal fin is present, which rules out every spined dogfish. Open the mouth and the genus name explains itself: Heterodontus means different teeth, and the front of each jaw carries small pointed cusps for gripping while the rear carries broad, pavement-like molars for crushing shell (more on how shark teeth work).
How big does the Japanese bullhead shark get?
This is a small shark. The largest reliably measured Japanese bullhead sharks are about 1.2 m (3.9 ft) in total length, and most adults on a reef are 80 cm to 1 m. Older accounts describing the species as "3.9 ft tall" have simply confused total length with height; nothing about this animal stands upright.
Weight has never been recorded systematically, which is worth admitting rather than guessing at. A metre-long bullhead shark is a stocky fish of a few kilograms, far lighter than its heavy-shouldered shape suggests, because the body tapers sharply behind the second dorsal fin. Hatchlings leave the egg case at roughly 18 cm, already banded and already crawling on their pectoral fins.
Males are sexually mature at about 69 cm. The length at which females mature has never been established, a gap that still appears in every modern account of the species, and it matters: without it, nobody can say how many years of growth a female needs before she starts laying. Females do grow slightly larger than males, as in all bullhead sharks, but the difference is modest. Put the maximum length beside the 1.8 m diver in the bar below and the scale of the animal is obvious.
Where Japanese bullhead sharks live
The species occupies a narrow strip of the north-western Pacific. Its core range runs from central and southern Japan, south of Hokkaido, across to the coasts of the Korean Peninsula and South Korea, then down the East China Sea along the coast of China to Taiwan. Nothing that can be trusted places it outside those seas; records from further south usually turn out to be other bullhead sharks.
Within that range it is a shallow-water animal, living between about 6 and 37 m (20 to 121 ft) on rocky reefs, boulder fields and kelp beds. It likes structure: ledges, gullies and the dark spaces under slabs, where it wedges itself during the day. Water temperature over most of the range runs from roughly 12 °C in the northern winter to 25 °C in the southern summer, and the sharks move deeper or further south as the surface cools.
Claims that the species reaches the deep sea are wrong, and so is the idea that it is a wanderer. Bullhead sharks are homebodies with small ranges and strong site attachment, which is exactly why local losses matter: the population that has largely disappeared from the Bohai Sea, in the far north-west of the range, is unlikely to be replaced by immigrants from Japan.
3 countries list the japanese bullhead shark in their species guide; the count is the number of incidents attributed to it there in the SharkSider database. Browse every guide on sharks around the world and sharks in the US.
What Japanese bullhead sharks eat
Everything about the head of this shark is built for armoured prey. Sea urchins are the staple, taken whole and reduced to gravel by the flat rear teeth; crabs, shrimps, gastropods, bivalves and small bottom fish make up the rest. The jaws are protrusible, so the shark can shoot them forward and suck a prey item off the rock rather than having to chase it, and the same suction pulls loose shell fragments in.
The hunting method is a slow patrol rather than a chase. The shark moves over the reef using its thick pectoral and pelvic fins as legs, planting one pair and then the other in a gait that genuinely deserves the word walking, and it will push its head into crevices to reach an urchin. Once the prey is in the mouth, the front teeth hold while the head shakes the animal free of the rock, and the molars take over.
Feeding is mostly nocturnal. During the day the shark lies wedged under a ledge, and the fact that it digests slowly means a single night of urchins can keep it going. This is the opposite of the constantly swimming, high-energy predators most people picture when they hear the word shark; and it is one reason a bullhead shark can live on a reef that would starve a fast predator.
Behaviour, senses and defences
Watch one for an hour and the impression is of an animal in no hurry at all. Japanese bullhead sharks are nocturnal, spending daylight jammed into a crevice or lying on sand beside a boulder, and becoming active after dusk. They are not social in any organised sense, but several will share a good reef and the same caves, and females gather at laying sites.
Swimming, when it happens, is laboured: the stiff body and small tail make this a poor distance swimmer, and the shark rarely leaves the bottom for long. Buoyancy helps — like all sharks it has a large oily liver instead of a swim bladder — but a bullhead shark is close to neutrally weighted and happy to sit still.
Its defences are passive and effective. The two dorsal spines make the shark awkward to swallow, and a predator that takes one head-first gets a mouthful of bone-hard points; this is the same arrangement that protects the Port Jackson shark in Australian waters. The thick skin and small, densely packed dermal denticles add armour. For senses, the shark relies on smell and on the electroreceptive pores of the ampullae of Lorenzini, which pick up the faint fields of buried molluscs; eyesight matters less on a dark reef, and the small eyes reflect that.
Eggs, nests and lifespan
The Japanese bullhead shark is oviparous, and its egg case is one of the strangest objects in the sea: a brown conical capsule wrapped in two broad spiral flanges, like a screw thread. The female produces them in pairs and lodges them in rock crevices or among kelp holdfasts, where the flanges lock the case in place against surge. Six to twelve eggs are laid over a season, mainly between March and September.
What makes the species unusual is that the females share their nurseries. Several will use the same sheltered ledge at around 8 to 9 m, so a single crevice can hold dozens of capsules of different ages, a habit known in only a handful of sharks. Incubation is long — close to a year — and the young emerge fully formed at about 18 cm, banded like miniature adults and immediately able to crawl.
Beyond that the life history is thin. Males mature at roughly 69 cm, female maturity is unrecorded, and no ageing study has produced a maximum age for the species. By comparison with better-studied bullhead sharks that live twenty to thirty years, a lifespan in that range is plausible, but plausible is not measured, and this page will not pretend otherwise. Our page on how long sharks live explains why vertebral ageing is so difficult in small bottom species.
Is the Japanese bullhead shark dangerous?
No. There is no record anywhere of a Japanese bullhead shark injuring a swimmer, diver or snorkeller, and the SharkSider database holds none either. The animal is a metre long at most, spends its days asleep under a rock, and has a mouth built to crush urchins rather than to cut. A person could swim past one all day without the shark reacting.
The only realistic way to get hurt by one is to pick it up. Handled roughly, a bullhead shark twists, and the spines in front of its dorsal fins can puncture a palm — the same injury aquarium staff and fishermen occasionally take from a horn shark. That is a wound caused by the person, not an attack. Leave the shark where it lies and nothing happens. Japan's genuine bite record, such as it is, involves entirely different animals and is set out on our shark attacks in Japan page; the bullhead shark belongs instead on any honest list of the least dangerous sharks in the sea.
The SharkSider database has no incident attributed to this species. The database draws on the International Shark Attack File, the Global Shark Attack File and verified local reports, and is updated weekly.
Conservation status and threats
The IUCN Red List assesses the Japanese bullhead shark as Least Concern. It remains common through most of its range, it is not a target of any fishery, and it has no value in the fin trade because its fins are small and low quality. The species is not listed on CITES or on the Convention on Migratory Species, and no country gives it specific legal protection.
That does not mean it is untouched. The shark lives in some of the most heavily fished and most heavily developed coastal seas on earth, and it turns up as bycatch in bottom trawls, gillnets and traps set for other species. Where it is landed it is sold for meat, though in small quantities. The clearest warning sign is the Bohai Sea, in the northern Yellow Sea basin, where the species has largely vanished from catches — a combination of trawling pressure, habitat loss on rocky bottoms and warming water. Site-attached reef sharks recolonise slowly, if at all.
It is also a familiar animal in public aquariums in Japan, where it breeds readily and the spiral egg cases are often on display. Captive populations are useful for education and for basic biology, but they are no substitute for the reefs; see our notes on sharks in captivity and on why so many shark species are in trouble.
Close relatives and look-alikes
The Japanese bullhead shark belongs to Heterodontus, a genus of nine or so living species that is the only genus in the entire order Heterodontiformes — one of the eight orders of sharks, and the one with the fewest members. Its nearest neighbour geographically is the zebra bullhead shark, which overlaps with it in Japanese and Chinese waters and is told apart instantly by its many narrow black stripes on a cream ground. The crested bullhead shark and the Port Jackson shark of Australia are larger, with much higher brow ridges, and the Port Jackson adds a harness-like dark marking across the shoulders. The whitespotted bullhead shark of the Arabian Sea and the Galapagos bullhead shark of the eastern Pacific are both spotted rather than banded.
Among sharks that are not relatives at all, the one most often confused with it on a Japanese reef is the Japanese angelshark, which is flat and ray-like and lies half-buried in sand rather than wedged under rock, and the cloudy catshark, a slender brown catshark with a long tail and no fin spines. If the shark you are looking at has a spine in front of each dorsal fin and a face like a pig, it is a bullhead.
Zebra Bullhead Shark (Heterodontus Zebra)species profile
Crested Bullhead Sharkspecies profile
Port Jackson Sharkspecies profile
The Horn Sharkspecies profile- Whitespotted Bullhead Sharkspecies profile
Galapagos Bullhead Sharkspecies profile
Frequently asked questions
How big do Japanese bullhead sharks get?
They reach about 1.2 m (3.9 ft) in total length, and most adults on the reef measure 80 cm to 1 m. Hatchlings emerge from the egg case at roughly 18 cm. Males mature at about 69 cm; the size at which females mature has never been established. No maximum weight has been published.
Where does the Japanese bullhead shark live?
Only in the north-western Pacific: southern and central Japan, the Korean Peninsula, the East China Sea along the Chinese coast, and Taiwan. It stays on rocky reefs, boulder fields and kelp beds between about 6 and 37 m, and does not occur in deep water or outside those seas.
What do Japanese bullhead sharks eat?
Mainly sea urchins, which they crush with the broad molar-like teeth at the back of the jaws. Crabs, shrimps, snails, clams and small bottom-living fish make up the rest. They feed at night, using protrusible jaws to suck prey off the rock, and they digest slowly enough to skip meals.
Are Japanese bullhead sharks dangerous to humans?
No. There is no recorded incident of one injuring a person, and the SharkSider database holds none. The shark is small, slow and sleeps under ledges by day. The only real risk is self-inflicted: the stout spines in front of the dorsal fins can puncture a hand if the animal is picked up.
Why is it called a bullhead shark?
Because of the head shape: short, broad and blunt, with ridges above the eyes that give a heavy-browed look. The scientific name points at the teeth instead. Heterodontus means different teeth, describing jaws that carry small pointed grasping cusps in front and flat crushing plates behind.
How do Japanese bullhead sharks reproduce?
They lay eggs. Each capsule is a brown cone wrapped in two spiral flanges that screw it into a crevice, and a female lays six to twelve per season, mostly between March and September. Several females use the same sheltered ledge, so one crevice may hold dozens of egg cases.
How long do the eggs take to hatch?
About a year. The long incubation is normal for bullhead sharks and reflects cool water and slow embryonic development. The young break out at roughly 18 cm, already carrying the adult banding and the dorsal spines, and they begin crawling across the reef on their pectoral fins almost at once.
Do Japanese bullhead sharks really walk?
In effect, yes. The thick, muscular pectoral and pelvic fins are planted alternately against the bottom so the shark clambers over rock rather than swimming above it. The gait lets it work into crevices after urchins and shellfish, and it is far cheaper in energy than constant swimming.
Are Japanese bullhead sharks endangered?
The IUCN lists them as Least Concern, and they remain common in Japanese and Korean waters. They are not targeted by fisheries and have no value in the fin trade. The concern is regional: the species has largely disappeared from the Bohai Sea, and site-attached reef sharks recover slowly.
Can you keep a Japanese bullhead shark in an aquarium?
Public aquariums in Japan keep and breed them regularly, and the spiral egg cases are a common exhibit. They are not a home aquarium animal: a metre-long shark needs a very large chilled tank, a hard-shelled diet and expert care, and taking one from the wild is neither legal everywhere nor sensible.
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 August 22, 2022 · Last updated September 22, 2026 · No incident attributed to this species in the SharkSider attack database, which is updated weekly.
