The Viper dogfish or Viper shark (Trigonognathus kabeyai) is a rare species of shark belonging to the family Etmopteridae, and the only extant member of its genus. It has been found in the Pacific Ocean off southern Japan, the Bonin Islands, Pacific Ocean off northern Taitung County and the Northwestern Hawaiian Islands. They can be found on the upper continental slopes and seamounts, participating in diel vertical migration. The Viper dogfish captures prey by protruding its jaws and impaling them with its long, curved fang-like teeth. Its remarkable gape allows it to swallow relatively large fish whole.
Family: Etmopteridae – Lantern Sharks
Genus: Trigonognathus
Species: kabeyai
Phylum– Chordata
Class– Chondrichthyles
Subclass– Elasmobranchii
Common Name– Dogfish Sharks
Family– Etmopteridae
Common Name– Lantern Sharks
Genus– Trigonognathus
Species– kabeyai
Status: IUCN Red List DATA DEFICIENT
Average Size and Length: Mature males are between 37cm/1.2 feet-44 cm/1.4 feet. Mature females are 1.4 feet or larger. The maximum is at least 44 cm. The longest male was 47 cm/1.5 feet. The longest female was 54 cm/ 1.8 feet long.
Average Weight: The largest male weighed 0.43 kg /0.95 lb. The largest female weighed 0.76 kg /1.7 lb.
Current Rare Mythical Sightings: The first specimens of the Viper dogfish were 2 immature males caught off southern Japan by the bottom trawler Seiryo-Maru in 1986. The holotype, measured 22 cm/8.7 inches long and was collected off Cape Shiono at a depth of 330 m /1,080 feet. The second measured 37 cm/15 inches long and was collected off Hiwasa, Tokushima at a depth of 360 m /1,180 feet. It was described as a new species and genus by University of Tokyo researchers Kenji Mochizuki and Fumio Ohe in a 1990 article for the Japanese Journal of Ichthyology.
Based on molecular clock estimation, Trigonognathus is thought to have originated around 41 million years ago during the Middle Eocene, as part of a larger evolutionary radiation of etmopterid genera. One extinct species is T. virginiae, whose fossilized teeth have been recovered from Lutetian age (47.8–41.3 Mya) strata in Landes, southwestern France, and represents this genus.
Teeth and Jaw: The mouth of the Viper dogfish is long, narrow and terminal that looks snake-like. There are well-spaced, very big curved, fang-like teeth in front of both protrusible jaws. The most anterior teeth are grooved lengthwise. There are 6 to 10 upper, and 7 to 10 lower tooth rows occurring on each side, along with a single tooth row at the upper and lower symphyses (jaw midpoints). The teeth are largest at the symphysis and decline in size towards the corners of the mouth. When the mouth is closed, the upper symphysial tooth overlaps the lower, while the lateral teeth interlock. There is a deep pocket around the front of the upper jaws, opening to a very large gape. The mouth, teeth and jaw are designed to impale and swallow whole. The skeletal and muscular structure of its head shows unique features that support this feeding mechanism, which is unlike that of other sharks in its family and order.
Head: The head of the Viper dogfish is somewhat flattened. The snout is blunt and short. The nostrils are nearly vertical slits. The eyes are large and oval with Large spiracles that are diagonally elongated in a narrow elliptical shape. There is a translucent patch of photophores over the upper eyelid.
Denticles: The skin of the Viper dogfish, excluding on the fins, is densely covered with irregularly arranged, nonoverlapping dermal denticles. Each denticle has an enflamed rhombic shape with 10–40 facets on the crown.
Tail: There are photomarks with light-emitting photophores on the caudal peduncle and caudal fin. The caudal peduncle lacks keels or notches. The upper lobe of the caudal fin is larger than the lower and has a notch in the trailing margin.
Demographic, Distribution, Habitat, Environment and Range: The Viper dogfish can be found in the north and central Pacific in Japan, the Bonin Islands, northern Taitung County, and the Hawaiian Islands. They can be found on the bottom of the upper continental slopes between 1,083-1,181 feet. They can also be found on the uppermost slope of the seamount at 886 feet and are possibly oceanic. One Viper dogfish was caught from the Hancock Seamount, located about 190 miles northwest of Kure Atoll in the northwestern Hawaiian Islands. They may participate in diel vertical migration, traveling up to 492 feet at night, more than likely to hunt prey.
Diet: They more than likely eat large bony fish and crustaceans such as lanternfish. They can consume fish close to 40% as long as itself.
A number of Viper dogfish were recovered from the stomachs of predatory fishes caught in the Bonin Islands. Known predators of the Viper dogfish include the Bigeye tuna (Thunnus obesus) and the Sickle pomfret (Taractichthys steindachneri).
Ram-Suction Index: Ram. The jaws protrude to pierce or impale large prey with the large, curved fang-like teeth, then they swallow the prey whole with a very large gaping mouth, much like the attack of a snake.
Aesthetic Identification: The Viper dogfish has a cylindrical and slender body, and is dark brown dorsally and black ventrally with light-emitting photophores. There are 5 gill slits with the fifth gill slit being the longest. The fins are small and very thin, almost translucent. The pectoral fins are rounded and lobe-like. The two dorsal fins are positioned about between the pectoral and pelvic fins. Each dorsal fin has a slightly grooved spine in front. The second dorsal spine is longer than the first. There is no anal fin.
Biology and Reproduction: The Viper dogfish is bioluminescent. More than likely its ability to emit light is used in counter illumination and or in social communication or to confuse prey.
They are more than likely ovoviviparous. Research suggests that they give birth to less than 26 pups per litter. Males and females are thought to mature sexually at roughly 43 cm/1.4 feet and 52 cm/1.7 feet long.
The Viper dogfish is the only dogfish species that lacks a suborbital muscle, which is normally responsible for pulling the jaws forward when biting. Jaw protrusion is instead affected by the hyomandibular bone, which is articulated to the skull in a manner that allows it to swing down and forward. This unique arrangement serves to increase the distance the shark can protrude its jaws, as well as the size of its gape both vertically and horizontally. This is a unique biological characteristic for the Viper dogfish. (Shirai, S.; Okamura, O. (1992). “Anatomy of Trigonognathus kabeyai, with comments on feeding mechanism and phylogenetic relationships (Elasmobranchii, Squalidae)“. Japanese Journal of Ichthyology. 39 (2): 139–150.)
Behavioral Traits, Sensing and Intelligence: They have specialized adaptations to hunt and capture larger prey and perform unique migration patterns to capture prey.
Viper Dogfish Future and Conservation: There is not enough data to evaluate because population numbers are unknown, but they are rare and localized. Small numbers of Viper dogfish are caught incidentally in purse seines and bottom trawls as bycatch. They are of no commercial value.
Viper Dogfish Recorded Attacks on Humans: Not a threat to humans.