Pacific Hatchetfish, Argyropelecus affinis

Pacific Hatchetfish, Argyropelecus affinis. Fish collected in a deep water trawl net off Point Loma, California, August 2010. Length: 6.7 cm (2.6 inches). Collection and identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, Calaifornia.

The Pacific Hatchetfish, Argyropelecus affinis, is a member of the Marine Hatchetfish or Sternoptychidae Family, and is known in Mexico as pez hacha laminado. Globally, there are 7 species in the genus Argyropelecus, all of which are found in Mexican waters of the Atlantic and the Pacific Oceans.

The Pacific Hatchetfish has a disc-shaped and laterally compressed body that tapers toward the end. They are silvery with a black band dorsally. Their anal, caudal, and dorsal fins are transparent and their caudal base is long and narrow. Their head is short and features a vertical mouth and tubular eyes directed upward. They have a short spine in front of their gill covers and a prominent row of photophores along their underside. Their anal fin lacks spines and has 8 or 9 rays; their first dorsal fin has 9 rays; their second dorsal fin is a small adipose fin; their pectoral fin has 11 or 12 rays; and, their pelvic fins have 6 rays. They are covered with scales.

The Pacific Hatchetfish is a mesopelagic species found at depths between 274 m (900 feet) and 610 m (2,000 feet). They reach a maximum of 8.4 cm (3.3 inches) in length. They are known to make short vertical migrations and consume arrow worms, copepods, krill, ostracods, plankton, and salps. Reproduction is oviparous with planktonic eggs and larvae. They are believed to have a lifespan of less than 1 year. The Pacific Hatchetfish is poorly studied and very little is known about their behavioral patterns.

The Pacific Hatchetfish is a resident of all Mexican waters of the Pacific Ocean.

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

From a conservation perspective the Pacific 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.