Portuguese Dogfish

• Maximum lengthAbout 1.22 m (4 ft); most adults 80–110 cm; Mediterranean animals smaller
• WeightNo reliable published maximum; a 1 m adult weighs roughly 8–10 kg (18–22 lb)
• LifespanUnknown; no validated ageing method exists for the species
• Depth range150–3,675 m (490–12,060 ft); commonly 400–2,000 m
• DietSquid, deep-water bony fish, small sharks, cetacean carrion
• IUCN statusNear Threatened (assessed 2019)

How to recognise a Portuguese dogfish

Hauled up from a kilometre down, a Portuguese dogfish looks less like a shark than like a large, dark, rather flabby fish. The body is stout and cylindrical, the skin a uniform chocolate brown to near black, the snout short and bluntly rounded with the mouth close beneath it. The eyes are large and oval and shine green under a deck light, a reflective layer that gathers what little light and bioluminescence the deep sea offers.

The fins are the family's. Both dorsal fins are small and low, each with a tiny grooved spine at its front edge that is often hidden in the skin and easy to miss; the first dorsal begins well behind the pectorals. There is no anal fin, which at once rules out the catsharks and the six- and sevengills of the same depths, and the tail has a long upper lobe with a weak notch and a short lower lobe.

The scales settle the identification. In adults the dermal denticles are large, flat and almost circular, with a smooth surface and overlapping edges that make the skin look tiled; the species name coelolepis refers to the hollowed form of each scale. Juveniles have small three-pointed denticles instead, so a young fish can pass for a roughskin dogfish. The upper teeth are small and spear-shaped with a single narrow cusp; the lower teeth are broad, low blades with the cusp leaning sideways, locked together into a single cutting edge.

How big do Portuguese dogfish get?

Measured specimens top out at about 1.22 m (4 ft) in total length, and the old figure of 1.58 m that circulated in fishery literature has no verified specimen behind it, so this page treats 1.2 m as the maximum. Most adults landed in the north-east Atlantic are 80–110 cm, and females are the larger sex: in the fisheries west of Ireland and Scotland and off Portugal, females mature at about 100–105 cm and males at 85–90 cm.

Body size varies with place. Sharks from the western Mediterranean are markedly smaller than Atlantic ones and mature at correspondingly smaller sizes, probably because of the warm, food-poor deep water of that sea.

Weight has never been properly tabulated. A shark of this build weighs roughly 8–10 kg at 1 m, with a large share of that in the enormous oil-filled liver that keeps the animal neutrally buoyant; the liver can be a fifth or more of the total mass, which is precisely why the species was fished. Pups are 27–30 cm (11–12 in) at birth, already a quarter of adult length. The size bar below sets the 1.22 m maximum against a 1.8 m diver.

Where Portuguese dogfish live

The species was described in 1864 from a specimen landed in Portugal, and Portuguese slope waters remain one of its strongholds, but the range is far wider and distinctly patchy. In the eastern Atlantic it runs from Iceland and the Faroe Islands down the slopes west of Ireland and Scotland, the Bay of Biscay off France, Portugal, Madeira, the Azores and the mid-Atlantic ridge, then south along West Africa and to seamounts off southern Africa. In the western Atlantic it is known from the Grand Banks off Canada to Delaware Bay. It lives in the western and central Mediterranean, and in the Pacific off Japan, south-eastern Australia and New Zealand.

Depth defines it more than geography. Records begin at about 150 m, but that is exceptional; the species is common between 400 and 2,000 m on the continental slope and the deep plains beyond it, and a trawl at 3,675 m (12,060 ft) in the eastern Atlantic produced the deepest confirmed catch, placing the species among the very few sharks of the abyssal zone. Water there is 5–13 °C.

Genetics says the Atlantic population is a single well-mixed stock: samples from Ireland to South Africa and the Azores show high diversity but no structure, so adults must move freely along and across the ocean floor. Within that range the sharks sort themselves by depth: the smallest juveniles are found deepest, adults higher on the slope, and pregnant females shallowest of all.

What Portuguese dogfish eat and how they hunt

Stomachs from the Catalan slope, Portugal and the Rockall Trough tell a consistent story: this is a squid-eater first. Deep-water cephalopods make up the bulk of the diet by weight, followed by bony fish of the slope such as grenadiers, blue whiting, smoothheads and deep-water hake, with a scattering of other sharks, most of them small lanternsharks and squaloids, and the odd crustacean.

Two things about that list stand out. Many of the squid and fish are mid-water animals rather than bottom-dwellers, which means the shark must leave the sea floor to hunt, and a species once dismissed as a bottom-hugging sleeper is in fact a benthopelagic predator that rises into the water column. And the lower jaw's interlocking blades, combined with the small grasping upper teeth, are the tool kit of a shark that seizes prey it cannot swallow whole and cuts pieces from it, in the manner of the kitefin shark and the Greenland shark.

That cutting bite also makes the Portuguese dogfish a scavenger. Baited-camera and whale-fall studies in the North Atlantic have filmed the species gouging round plugs of blubber from sunken cetacean carcasses. In the dark it relies on smell and on the electrical sense, and the green-shining eyes suggest it also hunts the faint glow of bioluminescent prey.

Behaviour and life in the deep

Almost everything known about the living animal comes from what is left in trawl nets, a few submersible sightings and deep-sea camera landers. Those cameras show a slow, deliberate swimmer that cruises just above the bottom with unhurried beats of the tail, approaches bait from down-current, and can hold station for long minutes: sleeper-shark behaviour in the literal sense. Yet the mid-water squid in its stomach prove it can climb and hunt when it matters.

Buoyancy is the key adaptation. At 1,500 m a shark cannot afford to spend energy holding itself up, and the Portuguese dogfish solves the problem with a liver saturated in squalene, a hydrocarbon lighter than water, that brings the whole animal close to neutral buoyancy. The soft, poorly calcified skeleton and watery muscle do the same job by cutting weight. The cost is a slow metabolism and, almost certainly, a slow life.

The depth sorting by sex and size described above amounts to a large-scale segregation: males and females are caught in different proportions at different depths and places, and the shallower distribution of pregnant females suggests they move up the slope to give birth. Nothing is known of social behaviour. There is no evidence of bioluminescence in this species, unlike the lanternsharks that share its depths and appear in its diet.

Reproduction and lifespan

The Portuguese dogfish is aplacental viviparous, or ovoviviparous in older usage: the embryos develop inside the mother on the yolk of very large eggs, without a placenta, and are born fully formed. Litters range from 5 to 29, with a dozen or so typical, and the pups are 27–30 cm at birth. Pregnant females carry embryos at every stage in every month, so there is no breeding season, and the huge eggs and long development suggest a gestation of well over a year.

Maturity comes at 85–90 cm in males and 100–105 cm in females in Atlantic populations. How old that makes them is unknown. The tiny dorsal spines used to age other dogfish are useless here, and the vertebrae are too poorly calcified to read, so no validated age exists for the species. Everything about its biology, from the low fecundity to the slow growth of related sleeper sharks, points to a life measured in decades; the 70 years quoted on older pages is a guess, not a measurement (see how long sharks live).

Nursery grounds have never been located. Newborns and small juveniles are almost absent from the fisheries that catch adults, which, together with the depth sorting, suggests that pups are born in the deepest part of the range and stay there until they are large enough to move up the slope. A female may produce only a few litters in her life.

Is the Portuguese dogfish dangerous to people?

No. The SharkSider database has no incident attributed to the Portuguese dogfish, and there is no conceivable way one could arise: the species lives hundreds to thousands of metres below the surface, in water no swimmer or diver reaches, and comes into contact with people only on the deck of a trawler or longliner. Its bite is designed for cutting squid and blubber, and a hooked animal is too weak at the surface to use it.

The only hazards run the other way. Deep-sea sharks concentrate mercury and other metals in their flesh over a long life, so the salted and dried meat sold in Portugal and Japan is not something to eat often, and the fresh liver is rich enough in vitamin A to be toxic in quantity. Handling a landed shark is safe; the tiny dorsal spines are barely exposed and cannot deliver the painful jab that a spurdog's can.

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 the fishery

The IUCN Red List classes the Portuguese dogfish as Near Threatened globally, and its regional situation in European waters is considerably worse. The reason is a fishery that lasted decades and, in places, centuries. Portuguese longliners working the slope for black scabbardfish have landed the species since at least the nineteenth century, and from the late 1980s French and Scottish trawlers targeted it with the leafscale gulper shark west of the British Isles under the shared name siki, mainly for the squalene-rich liver oil used in cosmetics and supplements. Japan has fished it in Suruga Bay for liver oil since before the Second World War.

Survey catch rates in the north-east Atlantic fell sharply through the 1990s and 2000s, and because both siki species were landed together the decline was slow to register. The International Council for the Exploration of the Sea now advises zero catch. The European Union phased its deep-sea shark quota down to nil by 2010 and has kept it there, allowing only a small bycatch margin for the Portuguese artisanal longline fleet, and the North East Atlantic Fisheries Commission prohibits directed fishing in international waters. The species is not listed on CITES or the Convention on Migratory Species.

Whether the stock is recovering is unknown; a shark that may take decades to mature and bears a dozen pups every couple of years will show no quick response to protection, and continued bycatch in deep-water trawl and longline fisheries, plus a persistent liver-oil trade elsewhere, keeps the pressure on. Its story is a standard case in why sharks are endangered: exploited long before anyone measured how slowly it reproduces.

Similar species and close relatives

The closest relative is the roughskin dogfish (Centroscymnus owstonii), the only other member of the genus, which is slimmer, has a longer snout and keeps rough three-pointed denticles into adulthood. The longnose velvet dogfish (Centroselachus crepidater) shares the slopes and the dark colour but has a noticeably long snout and larger fin spines, and the velvet dogfish (Zameus squamulosus) is smaller with velvety skin. All are sleeper sharks, the family that also holds the giant Greenland shark, the Pacific sleeper shark and the little sleeper shark.

On a deck of mixed deep-water catch, the species most often confused with it is the leafscale gulper shark, its fishery partner, which is greyer, has a longer snout, a taller first dorsal fin and prominent spines, and belongs to a different family. The kitefin shark is similar in build and colour but has no dorsal spines at all and thick, fleshy lips. Turn the shark over and run a hand along its flank: the smooth, tiled scales of an adult Portuguese dogfish are unlike anything else in the net.

• Roughskin Dogfishspecies profile
• Longnose Velvet Dogfishspecies profile
• Velvet Dogfishspecies profile
• Greenland Sharkspecies profile
• Little Sleeper Sharkspecies profile
• Leafscale Gulper Sharkspecies 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.