Tropical Hatchetfish, Argyropelecus lychnus

Tropical Hatchetfish, Argyropelecus lychnus. Fish collected in a deep water trawl net off Point Loma, California, August 2010. Length: 2.5 cm (1.0 inch). Collection and identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.

The Tropical Hatchetfish, Argyropelecus lychnus, is a member of the Marine Hatchetfish or Sternoptychidae Family, and is known in Mexico as pez hacha plateado. Globally, there are seven species in the genus Argyropelecus, all of which are found in Mexican waters of the Atlantic and the Pacific Oceans.

The Tropical Hatchetfish has a disc-shaped and laterally compressed body that tapers toward the end. They are silvery in color with a black band dorsally. Their anal, caudal, and dorsal fins are transparent and their caudal fin base is long and narrow. Their head is short with a vertical mouth and large recessed eyes. There have 2 spines on their gill covers: the upper 1 is curved outward and the lower 1 points downward and is curved forward. They have a prominent row of photophores along their underside. Their anal fin has 7 spines and 5 rays; their first dorsal fin has 7 spines; their second dorsal fin has 9 rays; and, their pectoral fins have 11 rays. They are covered with scales.

The Tropical Hatchetfish is a mesopelagic species found at depths between 183 m (600 feet) and 610 m (2,000 feet). They reach a maximum 5.6 cm (2.3 inches) in length. They consume copepods and planktonic organisms. Reproduction is oviparous with planktonic eggs and larvae. They are believed to have lifespans of less than one year. The Tropical Hatchetfish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The Tropical Hatchetfish is a resident of all Mexican waters of the Atlantic and the Pacific Oceans.

The Tropical Hatchetfish is most likely confused with the Pacific Hatchetfish, Argyropelecus affinis (extended oval body; long tail base).

From a conservation perspective the Tropical Hatchetfish is currently considered to be of Least Concern with stable, widely distributed populations. They are common but small in stature, found in very deep waters, and seldom seen by humans and thus are of limited interest to most.