| Anotopterus | |
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| Anotopterus sp. (2008) | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Aulopiformes |
| Family: | Anotopteridae Zugmayer, 1911 |
| Genus: | Anotopterus Zugmayer, 1911 |
The daggertooths (genus Anotopterus) are a genus of marine mesopelagic fish in the order Aulopiformes, the sole genus of the family Anotopteridae. They are found in oceans worldwide, but prefer cooler waters. [1]
Daggertooths are similar in appearance to the related lancetfishes and barracudina. They are elongate, silvery, predatory marine fishes that lack scales and have sharp teeth likely used for hunting fishes. However, as their scientific name (meaning "without fins on its back") suggests, they lack dorsal fins which easily differentiates them from their close allies, especially the similar-looking lancetfishes. Another feature that distinguishes daggertooths from lancetfishes is the placement of the large, fang-like teeth. In lancetfishes, the fangs appear on both the upper and lower jaws while in daggertooths the fangs are only seen along the upper jaw. Whether the fangs or the distinctly protruding mandible inspired the common name "daggertooth" remains unclear. Anotopterus spp. have been reported to grow to as long as 147 cm (4.82 ft). The skin of daggertooths makes them highly refractive to light. Like their close relatives, they lack swim bladders.
The currently recognized species in this genus are: [2]
Anotopterus has long been considered a unique taxonomic family with close affinity to the families Paralepididae and Alepisauridae. Recent Bayesian assessment of fossil records, taxonomic relationships and four key molecular markers have determined a much closer kinship between Anotopterus to basal Paralepididae, like Magnisudis spp., with the implication being that the genus Anotopterus might more appropriately be considered a member of the barracudina family, Paralepididae. [3]
The form of Anotopterus suggests that of a swift swimmer, at least of a fish that can dart through water quickly for short distances, like some of its closest relatives in Paralepididae have been reported to do. Like its close cousins, it is likely that these fishes readily avoid collecting nets at the depths they most frequently occur in the mesopelagic, especially larger individuals. Daggertooth are predators of other fishes and are prey to larger fishes including its close cousins the lancetfishes. [4]
Very little is known about the feeding habits of daggertooths, although they have been said to eat young Pacific salmon, barracudina, and other mesopelagic fishes and it is generally assumed that they predate the most abundant fishes available. This ignorance of diet is partly due to the potential prevalence of regurgitation among net caught specimens, where nearly 100% of net caught daggertooths were documented with completely empty stomachs, the supposed reason being the regurgitation of freshly eaten food upon capture in nets as a defense mechanism. [5] They are likely visually based predators and adult individuals can easily engulf relatively large prey, fishes with 20–30 cm fork length, whole due to their unattached pectoral girdles and distensible stomachs. Observations of slash marks on numerous young Pacific salmon in the northern Pacific prompted an investigation into the potential impact of daggertooth depredation on young salmon stocks by assessment of the tooth marks left on the salmon and estimations of daggertooth abundance. The subsequent findings showed that slashes from failed daggertooth attacks could be distinguished from failed lancetfish attacks by the placement of the tooth marks, as daggertooths only have fang-like teeth along their upper jaw while lancetfish have fang like teeth along both the upper and lower jaws. [5] Whether daggertooth have a significant impact on northern Pacific Salmon stock remained inconclusive. [6]
It has been noted that as daggertooths age their teeth begin to diminish and their stomachs and intestines atrophy while their gonads increase greatly in size. [4] This observed, ontogenetic shift hints to a potentially semelparous reproductive modality, while this aspect of life history has not yet been fully substantiated. Like their relatives, it is thought that daggertooths are simultaneous hermaphrodites while their spawning and actual reproductive behavior remains a mystery.
Hubbs et al., (1953) speculated that daggertooths have an anti-tropical distribution and live in temperate and boreal latitudes at either pole. [7] Later work investigating the distributional overlap between daggertooths and Pacific salmon (Oncorhynchus sp.) seemed to verify this assertion although some lack of findings pointed to a spotty distribution in certain pole-ward regions. [6] Counter to this assumption, however, are the findings of Kim et al. (1997) who discovered that daggertooths can comprise a sizable portion of the diets of deep diving tuna in certain areas of the tropical, west Pacific. [8] It is possible that the latitudinal distribution of daggertooths is anti-tropical in the epipelagic with preferred temperatures being available at depth worldwide, which would also explain the conservation of such few species with near global distributions. [9]
Salmon is the common name for several commercially important species of euryhaline ray-finned fish from the genera Salmo and Oncorhynchus of the family Salmonidae, native to tributaries of the North Atlantic (Salmo) and North Pacific (Oncorhynchus) basins. Other closely related fish in the same family include trout, char, grayling, whitefish, lenok and taimen, all coldwater fish of the subarctic and cooler temperate regions with some sporadic endorheic populations in Central Asia.
Barracudinas are any member of the marine mesopelagic fish family Paralepididae: 50 or so extant species are found almost worldwide in deep waters. Several genera are known only from fossils dating back to the Ypresian epoch.
Aulopiformes is a diverse order of marine ray-finned fish consisting of some 15 extant and several prehistoric families with about 45 genera and over 230 species. The common names grinners, lizardfishes and allies, or aulopiforms are sometimes used for this group. The scientific name means "Aulopus-shaped", from Aulopus + the standard fish order suffix "-formes". It ultimately derives from Ancient Greek aulós + Latin forma, the former in reference to the elongated shape of many aulopiforms.
Anotopterus nikparini is a species of fish in the family Anotopteridae, the daggertooths. It is native to the northern Pacific Ocean, where it occurs as far north as the Bering Sea and as far south as Japan and Baja California.
Fangtooths are beryciform fish of the family Anoplogastridae that live in the deep sea. The name is from the Greek anoplo, meaning "unarmed", and γαστήρ, meaning "stomach". With a worldwide distribution in tropical and cold-temperate waters, the family contains only two very similar species in one genus, with no known close relatives.
Lancetfishes are large oceanic predatory fishes in the genus Alepisaurus in the monogeneric family Alepisauridae.
Alepisaurus ferox, also known as the long snouted lancetfish, longnose lancetfish, or cannibal fish, is a species of lancetfish found in the ocean depths down to 1,830 m (6,000 ft). This species grows to 215 cm (85 in) in total length and a weight of 9 kg (20 lb).
Sabertooth or sabretooth fish are small, fierce-looking deep-sea aulopiform fish comprising the family Evermannellidae. The family is small, with just eight species in three genera represented; they are distributed throughout tropical to subtropical waters of the Atlantic, Indian, and Pacific Oceans.
Enchodus is an extinct genus of aulopiform ray-finned fish related to lancetfish and lizardfish. Species of Enchodus flourished during the Late Cretaceous, and there is some evidence that they may have survived to the Paleocene or Eocene; however, this may just represent reworked Cretaceous material.
The Pacific viperfish, Chauliodus macouni, is a predatory deep-sea fish found in the North Pacific. It is reported as being either mesopelagic or bathypelagic, with diel vertical migration to shallower waters. The Pacific viperfish is one of the nine different species that belong to the genus Chauliodus, the viperfish. The Pacific viperfish tend to be the largest of the species, typically reaching lengths of up to 1 foot and are considered an example of deep-sea gigantism. The length-weight relationship of the pacific viperfish varies with sex with females tending to be longer and heavier than males.
The black swallower is a species of deep sea fish in the family Chiasmodontidae. It is known for its ability to swallow fish larger than itself.
Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs.
A viperfish is any species of marine fish in the genus Chauliodus. Viperfishes are mostly found in the mesopelagic zone and are characterized by long, needle-like teeth and hinged lower jaws. A typical viperfish grows to lengths of 30 cm (12 in). Viperfishes undergo diel vertical migration and are found all around the world in tropical and temperate oceans. Viperfishes are capable of bioluminescence and possess photophores along the ventral side of their body, likely used to camouflage them by blending in with the less than 1% of light that reaches to below 200 meters depth.
The Ipnopidae are a family of fishes in the order Aulopiformes. They are small, slender fishes, with maximum length ranging from about 10 to 40 cm. They are found in temperate and tropical deep waters of the Atlantic, Indian, and Pacific Oceans.
Sloane's viperfish, Chauliodus sloani, is a predatory mesopelagic dragonfish found in waters across the world. The species was first described by German scientists Marcus Elieser Bloch and Johann Gottlob Schneider in their 1801 book Systema ichthyologiae: iconibus CX illustratum, volume 1. Female C. sloani reach maturity between 133 and 191 mm, while males likely reach maturity at slightly smaller body lengths. It has two rows of photophores along its ventral side. It is believed that C. sloani can adjust the intensity of bioluminescence of the ventral photophores to camouflage itself from predators that might see its shadow from below.
The pelagic thresher is a species of thresher shark, family Alopiidae; this group of sharks is characterized by the greatly elongated upper lobes of their caudal fins. The pelagic thresher occurs in the tropical and subtropical waters of the Indian and Pacific Oceans, usually far from shore, but occasionally entering coastal habitats. It is often confused with the common thresher, even in professional publications, but can be distinguished by the dark, rather than white, color over the bases of its pectoral fins. The smallest of the three thresher species, the pelagic thresher typically measures 3 m (10 ft) long.
Oncorhynchus rastrosus also known as the saber-toothed salmon, or spike-toothed salmon is an extinct species of salmon that lived along the Pacific coast of North America and Japan. They first appeared in the late Miocene in California, then died out some time during the Early Pliocene. They are members of the genus Oncorhynchus, which contains living pacific salmon.
Cimolichthys is an extinct genus of large predatory marine aulopiform fish known worldwide from the Late Cretaceous. It is the only member of the family Cimolichthyidae.
The pearleyes are a family, Scopelarchidae, of aulopiform fishes, distinguished by their unique visual system, with two retinas in each eye.
Magnisudis atlantica, the duckbill barracudina, is a fish belonging to the genus Magnisudis of the family Paralepididae. It is a carnivorous fish that is endemic to the Atlantic Ocean and to much of the southern and northern Pacific Ocean.
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