Longfin Catshark

• Maximum length48.5 cm (19 in)
• WeightNot recorded; a few hundred grams
• LifespanNot measured
• Depth rangeAbout 530–865 m (1,750–2,840 ft)
• DietSmall bony fish, crustaceans, squid
• IUCN statusLeast Concern (assessed 2020)

How to recognise a longfin catshark

Nothing about this shark shouts for attention, which is itself the first clue. It is uniformly brown to sooty black, slightly darker on the fin webs, with none of the saddles, spots or blotches that mark shallow-water catsharks such as the cloudy catshark. The body is slim and soft, the skin thin enough that a specimen handled roughly on deck loses patches of it, and the whole animal feels loose rather than muscular.

The fin that gives the species its English name is the one to check. The anal fin is remarkably long and low, running back along the underside for a distance greater than the space between the two dorsal fins and finishing almost at the origin of the tail fin. Set against it, the two dorsal fins are small and similar to one another, the second placed well behind the pelvic fins, and the caudal fin is narrow, long and held almost level with the body rather than angled upwards.

The head completes the identification. The snout is flattened and broadly rounded, widening towards the tip in the bell shape that many members of the genus Apristurus share, and the nostrils sit close together on its underside. The eyes are small horizontal ovals with a faint greenish reflection. The gill slits are conspicuously short, shorter than the eye, and the mouth is a broad arch filled with many rows of tiny teeth, each carrying a slender central point with one or two cusplets on either side.

How big does a longfin catshark get?

The largest measured longfin catshark on record is 48.5 cm (19 in) in total length, and there is no credible report of a larger one. That is a shark that would lie comfortably across an adult's forearm.

The species also matures at very nearly that size. Specimens examined from Japanese and Philippine trawls have been mature at roughly 44 to 48 cm, meaning an adult longfin catshark has almost no growing left to do once it starts to breed. Which sex grows larger is not settled; the sample of measured mature animals is small, and the published figures for males and females overlap so closely that any claim of clear dimorphism would be guesswork.

Weight has never been published, and a figure would be misleading if it were. Deep-slope catsharks carry weakly mineralised skeletons, watery muscle and a large, oil-filled liver that keeps them close to neutral buoyancy, so they weigh far less than a coastal shark of the same length. A full-grown longfin catshark is a light animal of a few hundred grams. Hatchling size has not been described either, and the honest position is that no one has yet caught one small enough to measure. On the scale bar below, set against a 1.8 m diver, the species barely registers, and that is a fair impression of the genus as a whole.

Where longfin catsharks live

Every confirmed record comes from the western Pacific. The species has been taken off southern Japan, in the East China Sea and the South China Sea off China, around the northern Philippines, and along the Kyushu-Palau Ridge, the long line of drowned seamounts running south from Japan. That places the known range between about 36°N and 8°N. Nothing attributed to this species has been confirmed from the eastern Pacific, the Indian Ocean or the Atlantic.

Vertically the picture is tight. Catches cluster between roughly 530 and 865 m, a band on the upper and middle continental slope well below the shelf break. That is deeper than any diver and deeper than most bottom-trawl fisheries in the region work, although the deep-water fleets that target grenadiers and slope shrimps do reach into it.

The habitat itself is soft sediment on a gentle gradient. There is no daylight at that depth, the water sits somewhere between about 4 and 8 °C, and the pressure is in the region of 60 to 85 atmospheres. Food arrives mostly as a slow rain of material from the productive surface layer far above. Our overview of where sharks live sets this kind of habitat against the reefs and surf zones that most people picture when they hear the word shark.

What longfin catsharks eat

Stomach contents reported for the species are small bony fish, crustaceans such as shrimps and mysids, and squid. That is the standard fare of a mid-slope catshark, and it matches the mouth exactly: a wide, weakly built arch with hundreds of small multi-pointed teeth suited to gripping soft-bodied prey whole. Nothing in the jaw of this animal is designed to cut, and nothing it eats needs cutting.

Hunting in permanent darkness is a problem of detection rather than speed. The underside of the broad flat snout is peppered with the pores of the ampullae of Lorenzini, electroreceptors that register the faint fields given off by the muscles and gills of a buried or motionless animal, so sweeping the snout slowly over sediment works something like passing a detector coil across sand. The lateral line registers water movement from anything that bolts, and smell narrows a long approach to carrion.

Scavenging almost certainly matters more than active pursuit. Baited cameras dropped on slopes of this depth across the western Pacific routinely draw small catsharks within an hour or two, and an animal living where food is thinly spread cannot afford to chase much. The realistic picture is a shark cruising at a walking pace a few centimetres above the mud, taking whatever small live prey it startles and whatever sunken carcass it happens on first.

How the longfin catshark lives

The old version of this page called the species sluggish and said it stays still most of the time. That is a reasonable reading of its build, but it is worth separating what the anatomy implies from what anyone has actually watched, because no longfin catshark has ever been filmed alive. Everything below is inference from the body and from close relatives, not observation.

The body is built for economy. A large liver loaded with low-density oil brings the shark close to neutral buoyancy, so hovering just off the bottom costs almost nothing, and the pale, watery muscle is suited to slow continuous cruising rather than bursts. The fins are broad and rounded, good for manoeuvring in a small space and poor for speed. In an environment where a meal may be days apart, spending as little energy as possible is the whole strategy.

Breathing does not require swimming either. A bottom-living catshark draws water in through the mouth and spiracles and pumps it over the gills while lying motionless, which is why it can wait on the sediment indefinitely; our page on how sharks breathe sets that against the ram ventilation of fast open-water sharks. Beyond this, honest answers are short. Nobody knows whether longfin catsharks move seasonally, whether they gather to lay eggs, or how far an individual ranges across the slope.

Reproduction and lifespan

The longfin catshark is oviparous, and the eggs are the best-documented part of its life. Females release them in pairs, one from each oviduct, sealed inside tough horny capsules roughly 5 to 7 cm long with a thick, ridged shell and tendrils at the corners that catch on whatever the sediment offers. The embryo inside draws on its yolk sac alone and receives nothing further from the mother. Of the strategies described on our page about how sharks reproduce, this is the oldest and the simplest.

Cold water makes it a slow business. Development rate in egg-laying sharks tracks temperature closely, and at the 4 to 8 °C of the slope a capsule can take many months to hatch, compared with six to ten months for shallow coastal catsharks in warmer water. How many eggs a female produces in a season, where on the slope she leaves them and how large the hatchlings are have all gone unrecorded.

Maturity arrives at about 44 to 48 cm, which is to say almost at maximum size. Lifespan has never been measured. No one has attempted a vertebral ageing study on this species, and the vertebrae of deepwater catsharks are so poorly calcified that the growth bands are hard to count even when someone tries. Small catsharks from shallow water generally reach ten to twenty-five years, and cold, slow-growing deep-sea relatives can reasonably be expected to live longer, but that is an expectation and not a figure; our guide to how long sharks live explains why these numbers are so hard to establish.

Is the longfin catshark dangerous?

No, and not by a narrow margin. The species lives between roughly 530 and 865 m, while recreational scuba diving stops at around 40 m and the deepest technical dives fall far short of the shallow end of its range. It grows to 48.5 cm and its teeth are two or three millimetres long, shaped to hold a shrimp. The SharkSider database holds no incident attributed to it, and there is no plausible way for one to arise.

The only people who ever handle one are the crews of deep-water trawlers and the researchers who sort their catch, and for them the worst outcome is a graze from the sandpaper skin. The species belongs firmly among the harmless deep-sea sharks listed on our page of the least dangerous sharks; anyone wanting to know which sharks actually matter in the seas off Japan or the Philippines should read the country pages instead of this one.

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 longfin catshark as Least Concern in 2020. The reasoning rests on depth and distribution rather than on any population count, because no count exists: the species occupies a band of slope that is only partly fished, it spans several thousand kilometres of the western Pacific margin, and there is no directed fishery for it anywhere in that range.

Where fishing and the shark do overlap, the species turns up as incidental catch in deep bottom trawls working for grenadiers, slope shrimps and other deep-water targets off Japan, Taiwan and the Philippines. It has no market value, which matters less than it sounds: a small soft-bodied shark hauled from 700 m is unlikely to survive the pressure and temperature change, so discarding it alive is largely a formality.

The realistic long-term concerns are shared across the region rather than specific to one catshark. Trawl fleets have been pushed steadily deeper as shelf stocks have thinned, which brings gear into water that was effectively a refuge, and the expansion of oxygen-poor layers in a warming ocean compresses the depth band available to slope animals. Any species that lays a few large eggs and grows slowly recovers slowly, which is the pattern set out on our page on why sharks are endangered. For now the listing is genuinely reassuring, and the honest caveat is that it describes a shark nobody is monitoring.

Relatives and look-alikes

The genus Apristurus holds around forty described species and is one of the hardest groups of sharks to identify, so much so that several species are separated only by snout proportions, the position of the first dorsal fin and the shape of the skin denticles under a microscope. In the same western Pacific waters the longfin catshark shares the slope with the Japanese catshark, a larger and stockier animal reaching about 70 cm, and with the tiny pale catshark of the Indonesian and Philippine deeps, which is only about 21 cm long when adult. The broadnose catshark of the Bay of Bengal fills a comparable role in the Indian Ocean.

On the other side of the Pacific the equivalents are the longnose catshark and the Panama ghost catshark, and in the deep north-eastern Atlantic the pale, ghostly white ghost catshark. The genus is the most widespread group of deep-water sharks on earth.

The species most likely to be confused with it in a Philippine trawl is not an Apristurus at all: the onefin catshark, the only shark in the world with a single dorsal fin, comes from the same deep Philippine grounds and is similar in size and colour, but the missing first dorsal settles the question instantly. A wider tour of the group is on our guide to the types of sharks.

• Japanese Catsharkspecies profile
• Pale Catsharkspecies profile
• Broadnose Catsharkspecies profile
• Longnose Catsharkspecies profile
• White Ghost Catsharkspecies profile
• Onefin Catsharkspecies 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 November 9, 2022 · Last updated September 22, 2026 · No incident attributed to this species in the SharkSider attack database, which is updated weekly.