Lancetfish
Encyclopedia
Lancetfishes are large ocean
ic predatory fishes in the genus Alepisaurus ("Scaleless lizard"), the only living genus in the family Alepisauridae.
Lancetfishes grow up to 2 metres (6.6 ft) in length. Very little is known about their biology
, even though they are widely distributed in all oceans, except the polar
sea
s. Specimens have been recorded as far north as Greenland
. They are often caught as by-catch for vessels long-lining for tuna
.
The generic
name is from Greek
a- meaning "without", lepis meaning "scale", and sauros meaning "lizard".
, soft-rayed from end to end, with an adipose fin behind it. The dorsal fin has 41 to 44 rays and occupies the greater length of the back. This fin is rounded in outline, about twice as high as the fish is deep, and can be depressed into a groove along the back. The body is slender, flattened from side to side, deepest at the gill cover
s, and tapers back to a slender caudal peduncle.
The mouth is wide, gaping to the back of the eye, and each jaw has two or three large fang-like teeth, in addition to numerous smaller teeth. The caudal fin is very deeply fork
ed; its upper lobe
is prolonged as a long filament, although most lancetfishes seem to lose this when captured. The anal fin originates under the last dorsal ray, and is deeply concave in outline. The ventral fins are about halfway between the anal and the tip of the snout, while the pectoral fins are considerably longer than the body is deep and are situated very low down on the sides. There are no scale
s, and the fins are exceedingly fragile.
:
The main difference between the two is the shape of the snout, which is long and pointed in A. ferox, and slightly shorter in A. brevirostris.
ic crustacean
s, squid
and salp
s, as well as other fish. They have also been shown to be cannibalistic. They are preyed upon by opah
, shark
s, albacore
, yellowfin tuna
, and fur seal
s.
There are no commercial fisheries for lancetfishes. Their flesh is watery and gelatinous and, although edible, would prove difficult to utilize. They are caught as bycatch
by tuna fisheries, and are seen as a pest
, taking bait intended for more valuable species. Anecdotal evidence suggesting that they have an aphrodisiac
effect is likely to be an urban myth.
The tetraphyllidea
n tapeworm Pelichnibothrium speciosum is a significant parasite of Longnose lancetfish. It seems that the species is an intermediate
or paratenic
host for the tapeworm (Scholz et al. 1998).
s of adolescents have been shown to be hermaphroditic
, although there is no evidence of functional hermaphroditism in adults. They are oviparous.
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
ic predatory fishes in the genus Alepisaurus ("Scaleless lizard"), the only living genus in the family Alepisauridae.
Lancetfishes grow up to 2 metres (6.6 ft) in length. Very little is known about their biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, even though they are widely distributed in all oceans, except the polar
Polar region
Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica...
sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...
s. Specimens have been recorded as far north as Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
. They are often caught as by-catch for vessels long-lining for tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
.
The generic
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
name is from Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
a- meaning "without", lepis meaning "scale", and sauros meaning "lizard".
Description
Lancetfishes possess a long and very high dorsal finDorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
, soft-rayed from end to end, with an adipose fin behind it. The dorsal fin has 41 to 44 rays and occupies the greater length of the back. This fin is rounded in outline, about twice as high as the fish is deep, and can be depressed into a groove along the back. The body is slender, flattened from side to side, deepest at the gill cover
Operculum (fish)
The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....
s, and tapers back to a slender caudal peduncle.
The mouth is wide, gaping to the back of the eye, and each jaw has two or three large fang-like teeth, in addition to numerous smaller teeth. The caudal fin is very deeply fork
Fork
As a piece of cutlery or kitchenware, a fork is a tool consisting of a handle with several narrow tines on one end. The fork, as an eating utensil, has been a feature primarily of the West, whereas in East Asia chopsticks have been more prevalent...
ed; its upper lobe
Lobe (anatomy)
In anatomy, a lobe is a clear anatomical division or extension that can be determined without the use of a microscope This is in contrast to a lobule, which is a clear division only visible histologically....
is prolonged as a long filament, although most lancetfishes seem to lose this when captured. The anal fin originates under the last dorsal ray, and is deeply concave in outline. The ventral fins are about halfway between the anal and the tip of the snout, while the pectoral fins are considerably longer than the body is deep and are situated very low down on the sides. There are no scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
s, and the fins are exceedingly fragile.
Species
There are currently only two recognised speciesSpecies
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
:
- Longnose lancetfish, Alepisaurus ferox Lowe, 1833
- Shortnose lancetfish, Alepisaurus brevirostris Gibbs 1960.
The main difference between the two is the shape of the snout, which is long and pointed in A. ferox, and slightly shorter in A. brevirostris.
Ecology
Lancetfish have large mouths and sharp teeth, indicating a predatory mode of life. Their watery muscle is not suited to fast swimming and long pursuit, so it is likely that they are ambush predators, using their narrow body profile and silvery colouration to conceal their presence, then use their large dorsal fin to generate large acceleration, and large mouth and teeth to engulf prey before it can escape. That said, stomach content studies have revealed that they feed mainly upon planktonPlankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
and salp
Salp
A salp or salpa is a barrel-shaped, planktonic tunicate. It moves by contracting, thus pumping water through its gelatinous body...
s, as well as other fish. They have also been shown to be cannibalistic. They are preyed upon by opah
Opah
Opah are large, colorful, deep-bodied pelagic Lampriform fish comprising the small family Lampridae . There are only two living species in a single genus: Lampris...
, shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s, albacore
Albacore
The albacore, Thunnus alalunga, is a type of tuna in the family Scombridae. This species is also called albacore fish, albacore tuna, albicore, longfin, albies, pigfish, tombo ahi, binnaga, Pacific albacore, German bonito , longfin tuna, longfin tunny, or even just tuna...
, yellowfin tuna
Yellowfin tuna
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.Yellowfin is often marketed as ahi, from its Hawaiian name ahi although the name ahi in Hawaiian also refers to the closely related bigeye tuna. The species name, albacares can lead to...
, and fur seal
Fur seal
Fur seals are any of nine species of pinnipeds in the Otariidae family. One species, the northern fur seal inhabits the North Pacific, while seven species in the Arctocephalus genus are found primarily in the Southern hemisphere...
s.
There are no commercial fisheries for lancetfishes. Their flesh is watery and gelatinous and, although edible, would prove difficult to utilize. They are caught as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
by tuna fisheries, and are seen as a pest
Pest (animal)
A pest is an animal which is detrimental to humans or human concerns. It is a loosely defined term, often overlapping with the related terms vermin, weeds, parasites and pathogens...
, taking bait intended for more valuable species. Anecdotal evidence suggesting that they have an aphrodisiac
Aphrodisiac
An aphrodisiac is a substance that increases sexual desire. The name comes from Aphrodite, the Greek goddess of sexuality and love. Throughout history, many foods, drinks, and behaviors have had a reputation for making sex more attainable and/or pleasurable...
effect is likely to be an urban myth.
The tetraphyllidea
Tetraphyllidea
Tetraphyllidea is a large tapeworm order that contains some 60 genera and about 800 described species. Tetraphyllideans are remarkable for their scolex morphologies, which are the most varied and morphologically complex amongst all tapeworm orders....
n tapeworm Pelichnibothrium speciosum is a significant parasite of Longnose lancetfish. It seems that the species is an intermediate
Intermediate host
A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host...
or paratenic
Paratenic
In parasitology, the term paratenic describes a host which is not needed for the development of the parasite, but nonetheless serves to maintain the life cycle of the parasite. Alaria americana may serve as an example: the so-called mesocercarial stages of this parasite reside in tadpoles, which...
host for the tapeworm (Scholz et al. 1998).
Reproduction
The reproductive system of lancetfish is something of a mystery. The gonadGonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s of adolescents have been shown to be hermaphroditic
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
, although there is no evidence of functional hermaphroditism in adults. They are oviparous.