''Argyropelecus sladeni'', or Sladen's hatchetfish, is a species of

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

in the family

Sternoptychidae The marine hatchetfishes or deep-sea hatchetfishes as well as the related bottlelights, pearlsides and constellationfishes are small deep-sea ray-finned fish of the stomiiform family Sternoptychidae. They are not closely related to and shoul ...

, found in the tropical and subtropical Atlantic, Indian and Pacific Oceans. This small fish lives in the

mesopelagic zone The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...

by day and makes a daily vertical migration to the

epipelagic zone The photic zone (or euphotic zone, epipelagic zone, or sunlight zone) is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological ...

at night.

Etymology

The fish is named in honor of British echinoderm biologist

Percy Sladen Walter Percy Sladen (30 June 1849 – 11 June 1900) was an English biologist who specialised in starfish. The son of a wealthy leather merchant, Sladen was born near Halifax, Yorkshire on 30 June 1849. He was educated at Hipperholme Grammar Sch ...

(1849-1900) and the Percy Sladen Memorial Trust, which funded the Indian Ocean expedition that collected the type species.

Description

''Argyropelecus sladeni'' is a small, deep-bodied hatchetfish with an abdominal keel and a maximum standard length of about . The mouth is of medium size, the tubular eyes point upwards, the dorsal fin has nine soft rays and is three times as long as it is high, and the adipose dorsal fin has a long base. The pectoral fins have 10 to 11 soft rays, the pelvic fins have 6 and the anal fin is in two parts, with seven soft rays in the front part and five behind. The upper pre-opercular spine is long and slopes upwards and backwards, while the lower one slopes downwards. There are two diagonally orientated post-abdominal spines, one blunt and forward pointing and the other backward pointing. The dorsal surface of the fish is dark, the flanks are silvery and there are

photophore A photophore is a specialized anatomical structure found in a variety of organisms that emits light through the process of boluminescence. This light may be produced endogenously by the organism itself (symbiotic) or generated through a mut ...

s (luminous spots) on the operculum and belly.

Distribution and habitat

This species has a circumglobal distribution in tropical and subtropical seas. The fish make daily vertical migrations; during the day their depth range is while at night it is . During the day, trawls at depths between produce the highest catches and at night the greatest abundance of fish is in the depth range .

Ecology

''Argyropelecus sladeni'' feed on

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic organisms,

krill Krill ''(Euphausiids)'' (: krill) are small and exclusively marine crustaceans of the order (biology), order Euphausiacea, found in all of the world's oceans. The name "krill" comes from the Norwegian language, Norwegian word ', meaning "small ...

amphipods Amphipoda () is an order (biology), order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphip ...

copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...

s and

ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

s. The species is

oviparous Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

and both eggs and larvae drift as part of the plankton.

Status

A common fish, ''A. sladeni'' is abundant in many parts of its wide range. No specific threats have been identified and the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

has rated its conservation status as being of "

least concern A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...

References

{{Taxonbar, from=Q2145852 Sternoptychidae Fish described in 1908 Bioluminescent fish Taxa named by Charles Tate Regan