Taillight Shark

• Maximum lengthAbout 52 cm (20 in), an adult female; males mature at 42–46 cm
• WeightNo measurement published; a few hundred grams
• LifespanUnknown; no ageing study exists
• Depth rangeNet records 195–641 m (640–2,100 ft); probably lives deeper by day
• DietUnknown; probably squid and small midwater fish
• IUCN statusLeast Concern (assessed 2018)

How to recognise a taillight shark

If a small dark shark comes up in a midwater net in the southern oceans, this is what to look for. The taillight shark is a compact animal, slightly flattened from side to side, with a long rounded snout and eyes so large and oval that they dominate the head. The mouth is wide for the size of the fish and the lips are thick and fringed, though unlike those of the cookiecutter shark they cannot form a sucker. The teeth follow the kitefin pattern: about 29 rows of small, narrow upper teeth and about 34 rows of much larger, blade-like lower teeth whose bases overlap into a single continuous cutting edge.

The colour is two-toned, dark brown above grading to black on the belly, with conspicuously paler fin edges. Tiny photophores, light-producing organs, are scattered over the skin, as in the pygmy shark and lanternsharks. The pectoral fins are large, rounded and paddle-shaped, quite unlike the narrow pointed pectorals of most small squaliform sharks. The first dorsal fin is small and sits midway between the pectorals and the pelvics; the second is larger and stands over the pelvic fins. Neither dorsal has a spine, there is no anal fin, and the caudal fin has a strong lower lobe and a long upper lobe notched near the tip.

Finally, on the underside just in front of the vent, lies the feature that names the species: a pouch of skin lined with yellowish papillae of luminous tissue. Squeeze a fresh specimen and it exudes a blue-glowing fluid.

How big is a taillight shark?

Small enough to hold in one hand. The largest known specimen is an adult female of about 51.5 cm (20 in). The two mature males on record measured 41.6 and 45.5 cm, and the very first specimen, the one that gave the species its name, was an immature female of just 17.6 cm. That is the entire size series, so nobody can say how much bigger a female can grow.

What the numbers do show is that males mature at around 42 to 46 cm and that females get larger, the usual pattern in dalatiid sharks. Size at birth is unknown, because no pregnant female has been examined; in the pygmy shark, its nearest relative, pups are born at roughly 6 to 10 cm, and a similar figure is likely here. No specimen has been weighed and reported, but a shark of this length and build would be a few hundred grams at most.

For scale, the taillight shark is about the length of a large man's forearm, far smaller than the kitefin shark at the top of its family (1.8 m) and larger than the pygmy and spined pygmy sharks, which top out around 22 to 27 cm. On the size bar below, its 52 cm maximum barely reaches the knee of a 1.8 m diver.

Where taillight sharks live

The known distribution is simply a list of capture sites. The first specimen was hauled up in 1963 by the Cape Town trawler Arum off the west coast of South Africa, and it was named by the South African ichthyologists Hulley and Penrith in 1966. The next came from the western South Atlantic off Uruguay, and the most recent records extend the species into the south-east Pacific off Chile, near the Juan Fernández Islands. Three sites thousands of kilometres apart almost certainly mean a continuous but thinly spread range across the temperate South Atlantic and southern Pacific, probably including waters off Argentina and Namibia where no one has yet caught one.

The nets that took the specimens were fishing at 195 to 205 m and at 458 to 641 m, over sea floors 1,000 m or more deep, but a trawl passes through every depth on its way up and down, so those figures bracket rather than pinpoint where the shark lives. Its large eyes, photophores and oceanic capture sites all point to a mesopelagic life in the open ocean, well away from the bottom, in water of roughly 5 to 12 °C. Like the pygmy shark it may rise towards the surface at night and sink by day. It has never been recorded over a continental shelf.

What taillight sharks eat

Honestly, nobody knows. No published study has examined the stomach contents of a taillight shark, and with so few specimens in museum jars, none has been sacrificed for the purpose. What can be said comes from the equipment. The jaws are strong for the size of the animal, the mouth is wide, and the lower teeth interlock into a saw-edged blade, the arrangement the kitefin shark and cookiecutter use to cut pieces out of prey larger than themselves. A shark built this way is not a picker of tiny crustaceans; it is a predator that bites chunks.

The likeliest prey in mid-water are squid, lanternfish and other small bioluminescent fishes. The huge eyes suggest the shark hunts by sight in the faint blue light that persists down to a few hundred metres, spotting a silhouette above or the glow of a photophore. Whether it also takes bites from animals bigger than itself, as a cookiecutter does from tuna and dolphins, is an open question; the fringed lips are not suctorial, which argues against it.

The luminous fluid may play a part in the hunt, either startling prey or drawing it towards the mouth, though defence is the likelier purpose. The pale fin margins and ventral photophores, seen from below, would break up the outline against the surface glow in the way that countershading does in shallow-water sharks.

Behaviour and the glowing pouch

Nothing of the taillight shark's behaviour has been observed alive, so this section is anatomy and inference. The organ that makes the species remarkable is a glandular pouch on the underside just ahead of the cloaca, opening through a slit. Its lining is folded into yellow papillae packed with luminous tissue, and when the pouch is squeezed it releases a fluid that glows blue in the dark. Many deep-sea squid and shrimps discharge glowing clouds as a defence, but among sharks the taillight is the only species known to do so. Lanternsharks and the pygmy shark glow from photophores fixed in the skin; they cannot squirt light.

The likeliest use is defence. A predator lunging at a 40 cm shark in the dark suddenly faces a bright, expanding cloud rather than a fish, and the shark slips away behind it. A role in hunting or in signalling to other taillight sharks has been proposed but cannot be tested until someone films a live animal. The body photophores probably work as in the pygmy shark, lighting the underside to match the dim glow from above and hiding the silhouette from anything looking up.

The paddle-like pectoral fins are the other oddity. Most small squaliform sharks have narrow pectorals and swim with the tail alone, but broad rounded fins can be sculled, and the taillight shark may row itself slowly through the water column. Its oil-rich liver gives near-neutral buoyancy, so hovering costs little. For the senses all sharks share, see the ampullae of Lorenzini.

Reproduction and lifespan

No pregnant taillight shark has ever been found, so its reproduction is inferred from its family. Every kitefin shark whose breeding is known is ovoviviparous: the eggs hatch inside the mother, the embryos live on their yolk sacs without a placenta, and a small litter of fully formed pups is born. The pygmy shark carries about eight pups and the cookiecutter six to twelve; a litter of that order is the reasonable expectation here.

What is known is the size at maturity. Both mature males on record, 41.6 and 45.5 cm, had fully developed claspers, and the 51.5 cm female was adult, so maturity comes at around 42 to 46 cm in males and somewhere below 52 cm in females. The 17.6 cm holotype was immature, and was in fact first described as a mature male before a closer look showed it to be a young female; it says something about how little material exists that the correction took years.

Nothing at all is known about gestation, breeding season, nurseries, growth rate or lifespan. Small deep-water squaliforms grow slowly and live longer than their size suggests, and the little that has been measured in the family points to lifespans of a decade or more (see how long sharks live). Until more specimens surface, every figure beyond the lengths above is a guess.

Is the taillight shark dangerous to people?

No, and it could not be. SharkSider's attack database has no entry of any kind for the taillight shark, and the reasons are plain: the animal is at most half a metre long, weighs a few hundred grams, and lives hundreds of metres down in the open ocean, far from any coast, diver or swimmer. Only a handful of scientists and trawler crews have ever handled one.

The one thing worth knowing if you ever do handle one is that the lower teeth are genuinely sharp, a miniature version of the kitefin blade, and that a fresh specimen may leak luminous fluid onto your hands. Neither is a hazard. For the handful of species that do injure people, and what to do about them, see how to survive a shark attack; the taillight shark is the opposite end of that spectrum.

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 assesses the taillight shark as Least Concern (2018). That seems odd for a species known from so few individuals, but the logic is sound: the Red List measures threat, not rarity of records, and the taillight shark lives in oceanic mid-water across a huge area of the southern hemisphere where there is almost no fishing at the depths it uses. Its size means it would slip through the mesh of most nets even where midwater trawls operate, and it has no commercial value. There is no evidence of decline and no plausible mechanism for one.

It is not listed on any CITES appendix or by the Convention on Migratory Species, and no country protects it by name; none needs to at present. The only real concern is ignorance. A species known from a handful of specimens cannot be monitored, and if deep midwater fisheries expand in the South Atlantic or south-east Pacific, the first sign of trouble would be hard to detect. Earlier assessments treated it as Data Deficient for exactly that reason.

For now the honest summary is that the taillight shark is probably safe because it is small, remote and unwanted. Its relatives on the continental slopes, where trawling and liver-oil fisheries reach, are a different story, covered under why sharks are endangered.

Similar species and close relatives

The taillight shark sits in the family Dalatiidae alongside some of the strangest small sharks in the sea. Its closest relative, reflected in the genus name, is the pygmy shark (Euprotomicrus bispinatus), a 27 cm oceanic shark with a similar dark body and pale fin edges but a bulbous snout, narrow pectorals, a tiny first dorsal set far back and no luminous pouch. The longnose pygmy shark (Heteroscymnoides marleyi) is the species the first taillight specimen was mistaken for; it shares the southern range but has a long conical snout and lacks the gland. The spined pygmy and smalleye pygmy sharks (Squaliolus) are smaller still, with a spine on the first dorsal fin, which the taillight never has.

The larger members of the family show what the taillight's jaws are for. The cookiecutter shark has the same interlocking lower blade but suctorial lips and a habit of gouging round plugs from whales and tuna; the kitefin shark is a 1.8 m slope predator with the family's dentition scaled up. Lanternsharks (Etmopterus), in a separate family, are the likeliest confusion in a net: also small, dark and photophore-studded, but every lanternshark has a spine in front of each dorsal fin. The paddle pectorals, the spineless fins and, above all, the pouch that glows when pressed settle it.

• Pygmy Sharkspecies profile
• Longnose Pygmy Sharkspecies profile
• Spined Pygmy Sharkspecies profile
• Smalleye Pygmy Sharkspecies profile
• Cookiecutter Sharkspecies profile
• Kitefin 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 September 13, 2022 · Last updated September 22, 2026 · No incident attributed to this species in the SharkSider attack database, which is updated weekly.