Longspine Hatchetfish, Sternoptyx diaphana
Longspine Hatchetfish, Sternoptyx diaphana. Fish collected in a deep water trawl net off Point Loma, California, August 2010. Length: 2.3 cm (0.9 inch). Collection and identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.
The Longspine Hatchetfish, Sternoptyx diaphana, is a member of the Marine Hatchetfish or Sternoptychidae Family, that is also known as the Diaphanous Hatchetfish and in Mexico as pez hacha luminoso. Globally, there are four species in the genus Sternoptyx, of which two are found in Mexican waters, one in both the Atlantic and the Pacific and one in the Pacific Ocean.
The Longspine Hatchetfish has a short deep body that is laterally compressed. Their body slopes up from the head and levels off at the tail base. They are dark dorsally transitioning to silvery on their sides. Their fins are transparent. There is a small translucent fold of skin just below their short tail and a large triangular transparent membrane above their anal fin. Their head has a short pointed snout with large eyes and a nearly vertical mouth. They have photophores behind and below their eyes, on their gill covers, and in rows on the underside of their body. Their anal fin has no spines and 12 to 16 rays; and, their dorsal fin has a toothed, pear-shaped translucent plate supported by a single spine and 9 to 11 rays.
The Longspine Hatchetfish is a bathypelagic species found at depths between 305 m (1,000 feet) and 1,524 m (5,000 feet). They live in dark, cold environments without plant life and with high water pressures, preferring water temperatures between 4oC (39oF) and 11oC (52oF). They reach a maximum length of 5.5 cm (2.2 inches). They are not vertical migrators and have limited pursuit capabilities, thus are opportunistic predators consuming amphipods, copepods, decapods, euphausiids, and small fish. They are believed to have a lifespan of less than one year. The Longspine 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 Longspine Hatchetfish is a resident of all Mexican waters of both the Atlantic and the Pacific Oceans.
The Longspine Hatchetfish cannot be confused with any other species due to its large transparent membrane above the anal fin.
From a conservation perspective the Longspine 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.