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Dorsal-fin rays 9; anal-fin rays 12; pectoral-fin rays 10–11; total gill rakers 17-21; vertebrae 35–37. Medium size species seldom exceeding 60 mm SL; body less deep, depth at of dorsal about two or times into SL; dorsal blade low, height about three or more times into its length; postabdominal spines of equal size, anterior one occasionally straight, usually squared or blunted; upper preopercle spine long, directed posteriorly and usually dorsally, lower directed ventrally and often slightly posteriorly; jaws medium; teeth small, recurved, no large canines present; gill rakers medium to long, slightly dentate; first preanal photophore raised well above second which is even with or above third; anal pterygiophore gap with three haemal spines lacking pterygiophores; in preservative pigment often quite dark; large distinct pigment spots present along midline, especially evident in smaller specimens; there may be a diurnal pigment difference similar to A. hemigymnus in this species.
Two separate postabdominal spines; anal subcaudal gap fewer than 2.0 times anal-preanal gap; dorsal rays. Both postabdominal spines of about equal length and size; anterior margin of posteriormost abdominal keel scale almost vertical; greater than 3.5 times body depth. No pair of enlarged canines in lower jaw; anteriormost postabdominal spine squared or blunt (except very small individuals), not curving evenly forward; upper preopercular spine extends well beyond posterior border of preopercle; no pigment on outermost caudal rays. Dorsal blade low, blade height less than 2.5 mm for 25–50 mm, less than 3.1 mm for 50-70 mm; body narrow; no spines on scales below subcaudal photophores; dark well-developed pigment spots forming line along posterior midline (especially in smaller sizes); upper preopercle spine usually curved.
In the Atlantic, this species is found in abundance along the African coast from about 15°S northward into the Gulf of Guinea; it occurs in moderate numbers across the equatorial Atlantic in a belt from 5°S to 15°N latitude; it is abundant in the Caribbean in the vicinity of the Venezuelan coast, absent from the northern Caribbean, appearing again in numbers in the western and northern Gulf of Mexico and the straits of Florida; a few small catches have been taken in the North Atlantic and along the Brazilian coast. In the Pacific a somewhat biantitropical distribution is indicated, with large populations represented in the North Pacific to about 175°W longitude, and off the California coast; another large population occurs off the coast of Chile; the species occurs north of New Zealand and south of Hawaii. A. sladeni is abundant in the northern Indian Ocean to about 15°and along the African coast to about 10° S; while not reported from the Bay of Bengal, it is represented by several small catches south of Java.
Concentrated between 350 m and 600 m by day, with the major concentrations between 350 m and 450 m; by night concentrated between 100 m and 375 m, with the major concentrations between 100 m and 300 m; no marked indication of geographic variation with depth.
Baird RC. 1971. The Systematics, Distribution, and Zoogeography of the Marine Hatchetfishes (family Sternoptychidae). Bulletin of the Museum of Comparative Zooology 142(1):1–128.
Baird RC. 1971. The Systematics, Distribution, and Zoogeography of the Marine Hatchetfishes (family Sternoptychidae). Bulletin of the Museum of Comparative Zooology 142(1):1–128.
Rarely exceed 60 mm SL.
Salomon Atoll, Chagos Archipelago, Indian Ocean [ca. 5°22'S 72°16'E], depth 400–500 fathoms.
Holotype: BMNH 1908.3.23.5.
Argyropelecus sladeni, or Sladen's hatchetfish, is a species of ray-finned fish in the family Sternoptychidae, found in the tropical and subtropical Atlantic, Indian and Pacific Oceans. This small fish lives in the mesopelagic zone by day and makes a daily vertical migration to the epipelagic zone at night.
The fish is named in honor of British echinoderm biologist Percy Sladen (1849-1900) and the Percy Sladen Memorial Trust, which funded the Indian Ocean expedition that collected the type species.[3]
Argyropelecus sladeni is a small, deep-bodied hachetfish with an abdominal keel and a maximum standard length of about 60 mm (2.4 in). 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 photophores (luminous spots) on the operculum and belly.[4]
This species has a circumglobal distribution in tropical and subtropical seas. The fish make daily vertical migrations; during the day their depth range is 350 to 600 m (1,100 to 2,000 ft) while at night it is 100 to 375 m (300 to 1,200 ft).[4] During the day, trawls at depths between 300 and 400 m (1,000 and 1,300 ft) produce the highest catches and at night the greatest abundance of fish is in the depth range 0 to 200 m (0 to 700 ft).[5]
Argyropelecus sladeni feed on planktonic organisms, krill, amphipods, copepods and ostracods.[5] The species is oviparous and both eggs and larvae drift as part of the plankton.[1]
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 has rated its conservation status as being of "least concern".[1]
Argyropelecus sladeni, or Sladen's hatchetfish, is a species of ray-finned fish in the family Sternoptychidae, found in the tropical and subtropical Atlantic, Indian and Pacific Oceans. This small fish lives in the mesopelagic zone by day and makes a daily vertical migration to the epipelagic zone at night.
