Longnose Lancetfish

## About

A deceased lancetfish.

The longnose lancetfish ***(Apelisaurus ferox)*** or long-snouted lancetfish, is a predatory fish species most common in tropical waters. The lancetfish is an exceedingly rare fish species that inhabits the midnight zone, the stretch of ocean that spans from 1-4km (0.62-2.4mi) deep. Lancetfish are very identifiable fish and have unique features such as; whitish-silver skin, large eyes, pronounced gill-slits and slender bodies. The most prominent feature of the body is the large sail on the lancetfish's back, which spans from just behind the head to the lower spine. Both the sail and the fins are a deep iridescent greyish-blue however, they may also appear brown or black. The characteristic sail can have up to 30-40 rays. Uniquely, lancetfish have no scales, rather they possess bare skin with pores. They also lack any form of swim bladder, a feature known throughout their order. The most noticeable feature of the longnose lancetfish is its narrow jaws, which gives it its name. A very unique feature of the longnose lancetfish is the lack of any form of sexual dimorphism, to a degree where both sexes have forms of male and female genitalia. This suggests the species is hermaphroditic. Longnose lancetfish can reach 0.97-2.15m (3.18-7ft) in length and can weigh between 1.3-9kg (2.9-20lbs), making them the largest species in their family.

## Diet

The longnose lancetfish are likely opportunistic ambush-hunters that are active most prolifically at daytime however, some researchers claim the fish are nocturnal. They hunt and eat cephalopods, tunicates and bony fishes however, the species has exhibited a preference for crustaceans, swimming crabs ***(Charybdis smithii)***, in particular. Though relatively uncommon, cannibalism occurs in the absence of other food sources. Through the examination of the varied stomach contents of lancetfish individuals, it was found likely that the species may migrate between depths and regions.

## Conservation Status

Though the longnose lancetfish is occasionally taken by bycatch, it is not commercially hunted. This is because it occurs at great depths and also because it is not seen as a favourable commercial fish species. Due to these factors, the lancetfish is thought to be a species of least concern by the IUCN.

## Range and Population

The longnose lancetfish is a widespread species that occurs in all of Earth's oceans, though, it is most common in sub-tropical and tropical conditions. Lancetfish occur as far north as Greenland and Iceland and as far south as Australia, New Zealand, South Africa and Chile. They are most common at the depths of 0-1.85km (1.15mi) in an area known commonly as the bathypelagic or midnight zone however, they are also frequent in the mesopelagic or twilight zone. It is thought that lancetfish may migrate between zones and regions -such as the subarctic- in the even of food scarcity. Currently no information has been quantified surrounding the lancetfish population or its status.

## Behaviour

Longnose lancetfish are rather enigmatic species and their behavioural characteristics have not been studied in full. Examining the anatomy of the lancetfish, it can be found that the species has an abundance of white muscles -and by principle a lack of many red muscles-, suggesting that the fish is only capable of short bursts of speed rather than cruising at a constant speed. This allows the longnose lancetfish to be incredibly agile and maneuverable. It is unknown whether lancetfish are nocturnal or not, with many conflicting reports surrounding this topic. It is known that adolescent lancetfish are synchronous hermaphrodites with both testes and oviducts. The sperm ducts are located internally just above the ovaries and both organs have separate external openings. Fertilisation occurs externally but it is unknown whether self-fertilisation is possible, or whether adults are also synchronous hermaphrodites. An enigmatic species, the lancetfish's breeding habits and age of sexual maturity are unknown. Some suggest the breeding season may occur in summer in the northern hemisphere, as lancetfish have been seen congregating off the coast of California, with young being caught around Bermuda. Young are known to be unreliant on their parents and adults may even cannibalise adolescent and juvenile individuals when food is scarce, giving the lancetfish the name; cannibal fish. As for sexual maturity, it is known that until a lancetfish reaches sexual maturity, their oviducts are covered by a connecting tissue.

### Relationship with Humans

Longnose lancetfish are greatly impacted by foreign pollution, with around 30% of the population commonly ingesting plastics. Micro plastics and rope fibres are most common among dissected individuals. Lancetfish are also commonly taken by bycatch, particularly in the Bay of Bengal, India, where they comprise 2% of all bycatch by circle and j-hook longlines. In the Philippines bycatch also seems quite severe, with some studies finding that fisheries caught more longnose lancetfish than tuna species. Unfortunately, only one third of lancetfish survive these encounters.

## In Captivity

No longnose lancetfish exist in captivity.

## Sources

* IUCN Red List of Threatened Species - https://www.iucnredlist.org/species/154820/4641606
* Alepisaurus ferox | Animal Diversity Web, University of Michigan Museum of Zoology - https://animaldiversity.org/accounts/Alepisaurus\_ferox/
* Alepisaurus ferox | Wikipedia - https://en.wikipedia.org/wiki/Alepisaurus\_ferox
* 11 Strange But True Facts About Lancetfish | NOAA Fisheries - https://www.fisheries.noaa.gov/feature-story/11-strange-true-facts-about-lancetfish