Sailfin Rough Shark

• Maximum length118 cm (3.9 ft)
• WeightNo reliable measurement; a few kilograms at most
• LifespanUnknown; not yet aged
• Depth range265–720 m (870–2,360 ft), mostly 500–600 m
• DietBottom invertebrates, small fish, shark and skate egg cases
• IUCN statusVulnerable (assessed 2020; Data Deficient in 2009)

How to recognise a sailfin roughshark

Nothing else in the North Atlantic is built like a roughshark. Seen head-on the body is a triangle: a narrow, ridged back rises steeply from a wide, flat belly, so the fish looks less like a shark than a keel with fins. On that ridge sit two dorsal fins so tall and broad that they gave the species its name; each one hides a spine at its leading edge, and in the sailfin the first spine leans backward. There is no anal fin, the tail is short and the pectoral fins are large and paddle-like.

The skin is the second signature. Instead of the fine, sandpaper texture of a dogfish, the sailfin wears large, widely spaced, thorn-shaped denticles that make it rasp-rough to the touch, which is what "roughshark" means. Colour is a uniform dark brown to black with no blotches, bands or pale lines.

The head is short with a blunt snout, and the mouth is small, transverse and framed by thick, fleshy lips. Behind each eye is a spiracle that is small and almost round; in the only other roughshark of these waters, the angular roughshark, the spiracle is a large vertical slit, the first dorsal spine leans forward, the colour is greyer with darker patches and the brow carries a knobbly ridge. Those four differences separate the two at a glance on a trawl deck. The teeth are unequal: small, spear-shaped points in the upper jaw and larger, blade-like triangles in the lower, in far fewer rows than a typical dogfish.

How big is a sailfin roughshark?

The largest sailfin roughshark on record measured 118 cm (3.9 ft) in total length, and that figure has stood for decades; nothing near the 1.5 m sometimes quoted for the family has ever been confirmed for this species. Most of the individuals that reach museums from trawl bycatch are between about 60 cm and 1 m, so a metre-long sailfin is a big one.

Weight has never been formally recorded for the species. The deep, laterally compressed body and the very large liver make roughsharks heavier than their length suggests, but for a 1 m fish that still means a few kilograms, not tens of them. Pups are about 25 cm (10 in) at birth, roughly a fifth of the maximum adult length, which is typical of sharks that give birth to well-developed young. The sizes at which males and females mature have not been established from an adequate sample, and there is no evidence of the strong size difference between the sexes seen in many requiem sharks. The size bar below sets the 118 cm maximum against a 1.8 m diver; a full-grown sailfin would reach a swimmer's waist.

Where sailfin roughsharks live

The sailfin roughshark is an eastern North Atlantic endemic. Its records run from the Hebridean slope west of Ireland and Scotland down through the Celtic Sea and the Bay of Biscay off France, along the Iberian slope off Spain and Portugal, and then south past Morocco, Western Sahara and Mauritania to Senegal. Specimens described in 2003 from the Azores pushed the known range well out onto the Mid-Atlantic Ridge, and it may occur on seamounts across the basin. It is absent from the Mediterranean, where the angular roughshark takes its place.

Depth is what defines its home. The confirmed range is 265 to 720 m (870 to 2,360 ft), and fishing records cluster between 500 and 600 m on the upper and middle continental slope, over mud and fine sand at temperatures of roughly 8 to 12 °C. It is almost never taken on the shelf, and the shallowest records are from the shelf edge. A suggested spring movement up-slope toward the shelf has been mentioned in the literature but has no tagging or seasonal catch data behind it.

The map below shows the slope band it occupies. The country pages linked above list the shallow-water sharks people actually meet on those coasts; the sailfin is not one of them.

What sailfin roughsharks eat

Honest answer first: no stomach-content study has ever been published for this species. What we can say comes from a handful of examined specimens and from the anatomy of the mouth, and it points to a slow bottom feeder taking small, soft prey: polychaete worms, small crustaceans, molluscs and the occasional small fish on the mud of the slope.

The best clue is the family's stranger habit. Its cousin the angular roughshark, kept in aquaria in Europe, presses its fleshy lips onto the egg cases of catsharks and skates, pierces them with the lower blade teeth and sucks out the yolk and embryo, and wild specimens have been caught with egg-case fragments inside. The sailfin has the same suction-cup mouth, the same thick lips and the same tooth arrangement, and it shares its depth with egg-laying sharks such as the blackmouth catshark and several deep-water skates, so egg predation is very likely part of its diet too.

There is no chase in any of this. A roughshark's body is built for hovering rather than sprinting, and the tiny mouth cannot take a prey item bigger than a finger. It cruises just above the bottom, finds food by smell and by the electroreceptors on its snout, and feeds by suction. Anything that requires speed is beyond it.

Behaviour and adaptations to the deep slope

Everything about the sailfin roughshark says slow. The compressed, high-backed body and the broad pectoral fins give it stability rather than speed, and it moves along the slope with an unhurried sculling of the short tail. In common with the other deep-water squaliforms, the kitefin and the Portuguese dogfish among them, it has an enormous liver rich in the low-density oil squalene, which brings it close to neutral buoyancy so that it can hang above the mud without spending energy on lift.

The two dorsal spines are its only defence. They are not venomous, but a thrashing roughshark on a deck can drive them into a hand, which is why deep-water fishermen handle the family with gloves. The rough denticles probably serve the same purpose against the few predators, mostly larger sharks, that share the slope.

Nothing is known about social behaviour, migration or activity rhythm; nobody has followed a live sailfin for more than the minutes it takes to sort a trawl. Catches are of single animals, which suggests a solitary life, and the absence of a strong seasonal signal in the records argues against long migrations. The senses are those of any shark, described on our shark anatomy page: large eyes tuned to the dim blue light that still reaches 500 m, a keen nose, and the ampullae of Lorenzini on the snout that let it find buried prey by its electric field.

Reproduction and lifespan

Like every roughshark, the sailfin is aplacental viviparous, which the older books call ovoviviparous: the eggs hatch inside the mother, the embryos live on their yolk sacs, and the pups are born fully formed at about 25 cm (10 in). That single number, the size at birth, is close to the sum of what has been published. Litter size has never been properly recorded for the species; the angular roughshark carries 7 to 23 pups, and a sailfin of similar build probably falls somewhere in that range, but that is inference, not data. Gestation, breeding season, nursery areas and the interval between litters are all unknown.

The same is true of growth. No vertebral ageing study exists, so there is no lifespan figure to give, and any number you see online for this species has been borrowed from a different shark. What can be said with confidence is what deep-water squaliforms in general show: slow growth, late maturity and small litters, which together mean a population that recovers slowly from any added mortality. Our page on how long sharks live explains why the deep-sea species tend to sit at the long end of the scale.

If you want a sense of how thin the record is, consider that the species was not described until 1929, from Portuguese waters, and that almost every specimen since has come dead from a net.

Are sailfin roughsharks dangerous?

No, and it would be hard to design a shark less able to hurt a person. It lives at 265 to 720 m, far below any diver, its mouth is a few centimetres wide and built for sucking yolk out of egg cases, and it swims too slowly to be a threat to anything that can move. The SharkSider database holds no incident attributed to the species, and there is no plausible way one could arise. Nobody has ever met a sailfin roughshark in the water; the only encounters happen on the decks of deep-water trawlers off Portugal, Spain, France and Scotland.

Those encounters are where the small real risk lies, and it runs the other way. The two dorsal spines are stout and sharp, the denticles rasp skin, and the lower teeth can cut a bare finger, so crew sorting a deep-water catch treat it with care. That is a handling injury, not a shark attack, and it is the only way this animal has ever drawn human blood.

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

The IUCN Red List assessed the sailfin roughshark as Vulnerable in 2020, on the basis of an inferred population decline from fishing. The previous assessment, in 2009, could only call it Data Deficient, and the change reflects better knowledge of the fisheries it meets rather than better knowledge of the shark itself: its entire depth band is worked by deep-water bottom trawls for hake, monkfish, blue whiting and deep-water shrimp off Iberia, in the Bay of Biscay and west of the British Isles, and every roughshark that enters those nets dies, whether it is landed or discarded. It has no commercial value beyond the occasional use as fishmeal.

The best protection it has is indirect. Since 2010 the European Union has set a zero total allowable catch for a list of deep-sea sharks, and Oxynotus paradoxus is on that list, so it may not be landed or sold from EU waters. Deep-water trawling below 800 m is also banned in EU Atlantic waters, though that limit sits below most of the sailfin's depth range, so the ban helps it less than it helps the gulper sharks such as the leafscale gulper. The species appears on no CITES or CMS appendix and has no protection off Morocco, Mauritania or Senegal, where the southern part of its range is fished with little observer coverage.

The honest bottom line is that no one can say whether the population is falling, because no one has counted it. That uncertainty, and the slow life history it shares with the rest of the deep-water sharks, is why it belongs in any discussion of why sharks are at risk and of the cost of bycatch.

Similar species and close relatives

The roughshark family holds five species, all in the genus Oxynotus and all instantly recognisable by the sail fins and the triangular body. The one you are most likely to confuse with the sailfin is the angular roughshark (O. centrina), which overlaps it off Iberia and West Africa but lives shallower, is grey with dark mottling, has a large slit-shaped spiracle and a forward-leaning first dorsal spine, and is the only roughshark of the Mediterranean. Across the Atlantic the Caribbean roughshark (O. caribbaeus) is smaller and patterned with dark saddles; in the south-west Pacific the prickly dogfish (O. bruniensis) is the roughshark of Australian and New Zealand slopes, and a Japanese species completes the set.

Beyond the family, the sailfin is a member of the dogfish order Squaliformes and shares its slope with several of them. The kitefin shark is larger, cylindrical and a genuine predator; the velvet belly lanternshark is small, glowing and abundant in the same trawls; the Portuguese dogfish lives deeper still. None of them could be mistaken for a roughshark once the fins are seen. One more link is worth knowing: the egg cases the roughsharks raid belong largely to catsharks such as the small-spotted catshark, whose shallow-water egg-laying is the reason the angular roughshark, rather than the deeper sailfin, is the species most often caught in the act.

• Angular Roughsharkspecies profile
• Caribbean Roughsharkspecies profile
• Prickly Dogfish Sharkspecies profile
• Kitefin Sharkspecies profile
• Velvet Belly Lanternsharkspecies profile
• Portuguese Dogfishspecies profile

Written and reviewed by

SharkSider Editorial Team

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 December 1, 2014 · Last updated September 22, 2026 · No incident attributed to this species in the SharkSider attack database, which is updated weekly.