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

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

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 should not ...

, 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, 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 proc ...

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 Sc ...

(1849-1900) and the

Percy Sladen Memorial Trust The Percy Sladen Memorial Trust is a trust fund administered by the Linnean Society of London for the support of scientific research. It was endowed by Constance Sladen, who was married to the marine biologist Percy Sladen (1849–1900), in his memo ...

, which funded the Indian Ocean expedition that collected the type species.

Description

''Argyropelecus sladeni'' is a small, deep-bodied hachetfish 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 glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors, ...

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 found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

ic organisms,

krill Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in n ...

amphipods Amphipoda is an 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 9,900 amphipod species so far descri ...

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 (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s and

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

s. The species is

oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...

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; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

has rated its conservation status as being of "

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

References

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