Pacific Hatchetfish, Argyropelecus affinis
The Pacific Hatchetfish, Argyropelecus affinis, whose common Spanish name is pez hacha laminado, is a member of the Marine Hatchetfish or Sternoptychidae Family, known collectively as peces hacha in Mexico. Globally, there are seven species in the genus Argyropelecus, all of which are found in Mexican waters of the Atlantic and the Pacific.
The Pacific Hatchetfish have disc-shaped and laterally compressed bodies that taper 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 are a mesopelagic species found at depths between 900 and 2,000 feet. They reach a maximum length of 8.4 cm (3.3 inches). They are known to make short vertical migrations and consume arrow worms, copepods, krill, ostracods, salps, and planktonic organisms. Reproduction is oviparous with planktonic eggs and larvae. They are believed to have a lifespan of less than one year. They are a poorly studied species and very little is known about their behavioral patterns.
The Pacific Hatchetfish are found in all Mexican waters of the Pacific.
The Pacific Hatchetfish is most likely confused with the Tropical Hatchetfish, Argyropelecus lychnus (oval body; shorter tail base).
The Pacific Hatchetfish are a small and very deep water species. They are abundant but seldom seen by humans. They are of limited interest to most. From a conservation perspective they are currently considered of Least Concern.
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, CA.