Lancetfish

:"For the United States Navy submarine, see USS Lancetfish (SS-296)" Taxobox
name = Lancetfishes
fossil_range = Middle Miocene - Present [cite journal
last = Sepkoski
first = Jack
authorlink =
coauthors =
title = A compendium of fossil marine animal genera
journal = Bulletins of American Paleontology
volume = 364
issue =
pages = p.560
publisher =
location =
date = 2002
url = http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=611&rank=class
doi =
id =
accessdate = 2008-01-08 ]


image_width = 250px
image_caption = Longnose lancetfish, "Alepisaurus ferox"
regnum = Animalia
phylum = Chordata
classis = Actinopterygii
ordo = Aulopiformes
familia = Alepisauridae
genus = "Alepisaurus"
genus_authority = Lowe, 1833
species = "A. ferox" "A. brevirostris"
binomial = "Alepisaurus ferox"
binomial_authority = Lowe, 1833
binomial2 = "Alepisaurus brevirostris"
binomial2_authority = Gibbs, 1960

Lancetfishes are large oceanic predatory fishes in the genus "Alepisaurus" ("Scaleless lizard"), the only living genus in the family Alepisauridae. [FishBase family | family = Alepisauridae | month = February | year = 2006]

They grow up to two metres long. Very little is known about their biology, even though they are widely distributed in all oceans, except the polar seas. [cite journal | author = T. Kubota & T. Uyeno | year = 1978 | title = On some meristic characters of lancetfish, "Alepisaurus", collected from Suruga Bay, Japan | journal = Journal of Faculty of Marine Science and Technology, Tokai University | volume = 11 | pages = 63–69] Specimens have been recorded as far north as Greenland. [cite journal | author = A. S. Jensen | year = 1948 | title = Contributions to the ichthyofauna of Greenland | journal = Spolia Zool. Mus. Havn. Shriff Univ. Zool. Mus. Københaven | volume = 9 | pages = 1–182] They are often caught as by-catch for vessels long-lining for tuna.

The generic name is from Greek "a-" meaning "without", "lepis" meanig "scale", and "sauros" meaning "lizard".

Morphology

Lancetfishes possess a long and very high dorsal fin, soft-rayed from end to end, with the presence of an adipose fin behind it. The dorsal fin has 41 to 44 rays, and occupies the greater length of the back, is rounded in outline, about twice as high as the fish is deep, and can be depressed in a groove along the back. The body is slender, laterally flattened, deepest at the gill covers, 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 fangs, besides smaller teeth. The adipose fin recalls that of the smelt in form and location. The caudal fin is very deeply forked; its upper lobe is prolonged as a long , and although most of the specimens 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 scales and the fins are exceedingly fragile.

pecies

There are currently two species recognised as valid:
* Longnose lancetfish, "Alepisaurus ferox" Lowe, 1833 [ITIS | ID = 162527 | taxon = Alepisaurus ferox | year = 2006 | date = 19 March] [FishBase species | genus = Alepisaurus | species = ferox | year = 2006 | month = February]
* Shortnose lancetfish, "Alepisaurus brevirostris" Gibbs 1960. [FishBase species | genus = Alepisaurus | species = brevirostris | year = 2006 | month = February]

The main difference 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 planktonic crustaceans, squid and salps, as well as other fish. They have also been shown to be cannibalistic. They are preyed upon by opah, sharks, albacore, yellowfin tuna, and fur seals.

There are no commercial fisheries for lancetfishes. Their flesh is watery and gelatinous and, although edible would prove difficult to utilise. 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 tetraphyllidean 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).

Reproduction

The reproductive system of lancetfish is something of a mystery. The gonads of adolescents have been shown to be hermaphroditic, although there is no evidence of functional hermaphroditism in adults. They are oviparous.

References

* Scholz, Tomáš; Euzet, Louis & Moravec, František (1998): Taxonomic status of "Pelichnibothrium speciosum" Monticelli, 1889 (Cestoda: Tetraphyllidea), a mysterious parasite of "Alepisaurus ferox" Lowe (Teleostei: Alepisauridae) and "Prionace glauca" (L.) (Euselachii: Carcharinidae). "Systematic Parasitology" 41(1): 1–8. doi|10.1023/A:1006091102174 (HTML abstract)

External links

* [http://www.abdn.ac.uk/~nhi991/alepisaurus.htm Parasites of Lancetfish]
* [http://www.gma.org/fogm/Alepisaurus_ferox.htm Presence of Lancetfish in the Gulf of Maine]