Idiacanthus fasciolaBlack Dragonfish(Also: Deepsea stalkeye fish)

Geographic Range

Idiacanthus fasciola is common in deep, temperate and equatorial oceanic waters. Specimens have been found throughout the northeast and central Atlantic Ocean as far north as 48° and in areas including the Grand Bank, Scotian Shelf, Gulf of Mexico, Straits of Florida and Caribbean Sea. It has been found in the southern Atlantic off Patagonia and as far south as 54°. In the eastern Atlantic, I. fasciola is common near the Azores, off Portugal, and off West Africa. Idiacanthus fasciola has also been found in the eastern and western Indian Ocean, off northern and eastern Australia, off Tasmania and in the western and equatorial Pacific Ocean. (; Gibbs, 1964; Nakamura, 1986; Scott, 1979; Whitehead, 1984)


Females inhabit depths of 500 to 2,000 meters during the day and travel up to 250 meters or shallower at night. Most males stay between 1000 and 2000 meters at all times and do not migrate. The smallest larvae are found in great depths (probably where adults spawn), but transitional larvae live in subsurface (350 meters or shallower) areas and move to greater depths during or shortly after metamorphosis. (Coad, 1995; Whitehead, 1984)

  • Range depth
    2000 to surface m
    6561.68 to ft

Physical Description

Adult I. fasciola females range from 19 to 48.9 cm. Adult males are strikingly different from females (described below) and are between 3 and 7 cm in length (Gibbs, 1964).

Idiacanthus fasciola has a long and sleek body that is 20 to 50 times longer than it is deep. The dorsal fin is also very long, extending along the posterior two-thirds of the length of the body, and with 54 to 80 rays. The anal fin is about half as long as the dorsal fin and contains 29 to 49 rays. Both the dorsal and the anal fins extend almost until the caudal fin. Both fins also have pairs of short, bony spines that border each ray. There are no adipose or pectoral fins, but pectoral fins are present in larvae. The pelvic fins (in females only) have 6 rays and are usually found closer to the head than the caudal fin.

The skin is black or very dark brown and without scales or markings in females. Males are described as dark brown and larvae are clear with rows of pigment marks (Gibbs, 1964). The post-orbital organ is pinkish.

The head of I. fasciola has a round snout, and proportionally small eyes (larger in males). The mouth is large and at an oblique angle and with premaxilla bones that are not protractible. Nostrils are located closer to the eye than to the mouth (Gibbs, 1964). Females have teeth in the jaws that are long, barbed and fang-like, vary in size and are depressible. The gill arches do not have rakers or teeth.

There is no lateral line present, but I. fasciola has two rows of photophores on both sides that extend along the ventral part of the body. Luminous material also flanks each dorsal and fin ray and is usually yellowish in color (Gibbs, 1964). There is also a post-orbital luminous organ, but no pre- or sub-orbital luminous organs (Nakamura, 1986).

There is a chin or hyoid barbel present in females that is about two and a half times the length of the head, (absent in males). This chin barbel has two forms: one with a bulblet on the end and one without.

Males are quite different from females as are adults from larvae. Although males are generally a similar overall shape as females, they do not exceed 7 cm in length. They lack teeth, chin barbells and pelvic fins. Their post-orbital organs are proportionally larger than in females, extending from slightly longer than the diameter of the eye to up to twice the diameter of the eye. Males also have a small extension (sperm duct) of flesh that originates near the anus and attaches to the modified first anal ray. (; Gibbs, 1964; Nakamura, 1986; Whitehead, 1984)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • ornamentation
  • Range length
    1.6 to 48.9 cm
    0.63 to 19.25 in


Idiacanthus fasciola goes through a remarkable metamorphosis from larva, postlarva, adolescent, transitional adolescent to adult. One common name for I. fasciola is the deep-sea stalkeye fish, which refers to the larval state. The larvae, which are long and slender and 1.6 to 2.8 cm in length, have eyes on the ends of proportionally very long, cartilaginous stalks that are up to 25% of the total body length. The eyestalks apparently allow for an increased range of vision (Weihs and Moser, 1981). The larvae do not have photophores and are clear except for a row of color spots. The head is long with no operculum and has a flat duck-like snout. The larvae have relatively large, paddle-like pectoral fins and no pelvic fins. The end of the intestine extends outside of the body and slightly beyond the caudal fin. In this early stage of development, the larvae are sexually indeterminate (Gibbs, 1964).

In the postlarval stage, 3.5 to 5.0 cm, I. fasciola begins to show adult and sexually dimorphic characteristics. The eyestalks begin to shorten and the cartilaginous rods coil up behind the eye. The head and snout begin to enlarge and the chin barbel and pelvic fins begin to grow in females.

In the adolescent stages, the skin darkens, eyestalks disappear, and the operculum grows to cover the gill openings. The intestine no longer extends beyond the caudal fin. In females, rapid growth occurs (can quadruple their length), teeth grow, and the chin barbel grows to the complete shape.

Males do not grow much in the adolescent stages and overall males retain some larval appearance in adult stage. But males do darken in these stages, the post-orbital organs grow as large or larger than the eye and the sperm duct grows out to the first anal ray. (Gibbs, 1964; Kawaguchi and Moser, 1983; Nelson, 1994; Weihs and Moser, 1981; Whitehead, 1984)


Idiacanthus fasciola is an oviparous species with external fertilization. Males have very large testes that take up most of their body cavity. There is a sperm duct that extend from the testes to the exterior of the body where it runs along and fuses with the first anal fin ray. This structure may be involved with the delivery of sperm, but the mobility of the structure is limited because it is fused with the ray (Gibbs, 1964).

Females have been found with ovaries that contain 14,000 mature eggs as well as many undeveloped eggs.

There is little information available on the mating behaviors of I. fasciola. (; Gibbs, 1964)

A rise in the collection of adult and immature females, as well as larvae, in the months of August and September suggest that this could be a breeding season. However, other collection data shows an even distribution of small specimens throughout the year, suggesting year-round breeding (Gibbs, 1964).

Collection results show larger specimens from greater depths, suggesting that adults may return to deeper waters for spawning. This is also where the smallest larvae are found. Little information is available on the reproductive behavior of I. fasciola. (Coad, 1995; Gibbs, 1964)

  • Breeding season
    There is some evidence that August and September are a breeding season, and other evidence that support year-round breeding.

There is no known information on the parental investment of I. fasciola.


Because adult males have a very diminished digestive tract, it is likely that their adult lifespan is quite short, possibly as short as a few weeks. Through collection numbers, it seems that females spend more time in the immature stages. Although they don’t seem to spend much time as mature adults, they probably live more than one year (Gibbs, 1964). (Gibbs, 1964)

  • Typical lifespan
    Status: wild
    1 (low) years
  • Average lifespan
    Status: wild
    >1 years


Schooling behavior is inferred from collection results. Larvae are often found together, suggesting that they school. Adults have been found in groups of 2 to 7, but it is not clear is this is a result of schooling behavior (Gibbs, 1964). (Gibbs, 1964)

Communication and Perception

Idiacanthus fasciola does not have a lateral line but does have many photophores. Larvae have eyes on eyestalks, perhaps to help them see better. There is no other information availalbe on perception and communication. (Gibbs, 1964; Weihs and Moser, 1981)

Food Habits

The food habits of I. fasciola are described in several sources as poorly known, but adults are known to eat mid-water fishes. A myctophid or lanternfish, from the genus Diaphus was found in an adult specimen (Gibbs, 1964). Remains of diatoms and small crustaceans have been found in postlarvae. Adult males lack a functional digestive track and diet (Coad, 1995). (Coad, 1995; Gibbs, 1964; Whitehead, 1984; Coad, 1995; Gibbs, 1964; Whitehead, 1984; Coad, 1995; Gibbs, 1964; Whitehead, 1984)


There is little information available on the predators of I. fasciola. However, a specimen of I. fasciola measuring 15.5 cm was found off the coast of Tasmania in the stomach of a deep-sea trevella or Hyperglyphe antarctica or Hyperglyphe porosa in 1978. (Scott, 1979)

Ecosystem Roles

There is little information available on role I. fasciola plays in ecosystems. However, because it is common in deep, temperate oceans, it seems to be an important part of these ecosystems. (; Fink, 1985)

Economic Importance for Humans: Positive

There are no known positive effects of I. fasciola on humans, but it is a fish that is apparently of great interest to some ichthyologists and students of biology.

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

There are no known negative effects of I. fasciola on humans.

Conservation Status

Idiacanthus fasciola is not listed as a threatened or endangered species on the IUCN, U.S. Federal List or CITES databases.

Other Comments

Idiacanthus fasciola was first described and named by Peters in 1876/1877.

Common names for I. fasciola include ribbon sawtailfish, black dragonfish and deepsea stalkeyefish.

The species Idiacanthus fasciola and genus Idiacanthus have gone through some classification changes over time. The remarkable stalkeye larvae of Idiacanthus fasciola were originally described as a separate species (Scott, 1979). Gibbs states that Idiacanthus is very closely related to Melanostomiatidae because they have nearly identical teeth structures. Idiacanthus is now considered the sister group to Tactostoma (Fink, 1983). The distinguishing characteristics of Idiacanthus fasciola are the extraordinary larval metamorphosis, very distinct sexual dimorphism, and pairs of spines that accompany the base of each dorsal and anal ray (Gibbs, 1964).

Many of the stomiatoid fishes have unique lower jaw barbels, although the function of this tissue is not clear. The chin or hyoid barbel found in I. fasciola females has been found to contain luminous cells (similar to those found in the photophores) near the end of the barbel. The end barbel also contains well-developed muscles, nerves and blood vessels (Hansen, 1970). (; Coad, 1995; Fink, 1983; Gibbs, 1964; Hansen, 1970; Coad, 1995; Fink, 1983; Gibbs, 1964; Hansen, 1970; Scott, 1979)


Anne Roecklein (author), University of Michigan-Ann Arbor, William Fink (editor, instructor), University of Michigan-Ann Arbor.

Matthew Wund (editor), University of Michigan-Ann Arbor.


Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map


Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


generates and uses light to communicate


an animal that mainly eats fish


"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


Coad, B. 1995. Encyclopedia of Canadian Fishes. Waterdown, Ontario: Canadian Museum of Nature and Canadian Sportfishing Production, Inc..

Fink, W. 1983. Stomiiformes: relationships. Ontogeny and Systematics of Fishes, 1: 181-184.

Fink, W. 1985. Phylogenetic Interrelationships of the Stomiid Fishes (Teleostei: Stomiiformes). Ann Arbor: Museum of Zoology, The University of Michigan.

Gibbs, R. 1964. Family Idiacanthidae. Pp. 512-521 in J Tee-Van, ed. Fishes of the western North Atlantic. New Haven: Yale University.

Hansen, K. 1970. On the luminous organs in the barbels of some Stomiatoid fishes. Meddr Dansk Naturh, 133: 69-84.

Kawaguchi, K., H. Moser. 1983. Stomiatoidea development. Ontogeny and Systematics of Fishes, 133: 169-181.

Krueger, W. 1990. Check-list of the fishes of the eastern tropical Atlantic. Paris: Unesco. Accessed October 14, 2004 at

Nakamura, I. 1986. Important Fishes Trawled off Patagonia. Japan: Japan Marine Fishery Resource Center.

Nelson, J. 1994. Fishes of the World. New York, NY: John Wiley & Sons, Inc..

Scott, E. 1979. Observations on some Tasmanian fishes : Part XXV. The Royal Society of Tasmania, 113: 99-105.

Weihs, D., H. Moser. 1981. Stalked eyes as an adaptation towards more efficient foraging in marine fish larvae. Bulletin of Marine Science, 31: 31-36.

Whitehead, P. 1984. Fishes of the North-eastern Atlantic and the Mediterranean. Paris: Unesco.