Longspine Hatchetfish, Sternoptyx diaphana
The Longspine Hatchetfish, Sternoptyx diaphana, whose common Spanish name is pez hacha luminoso, is a member of the Marine Hatchetfish or Sternoptychidae Family, known collectively as peces hacha in Mexico. This fish is also known as the Diaphanous Hatchetfish. Globally, there are four species in the genus Sternoptyx, two of which are found in Mexican waters, one in both the Atlantic and the Pacific and one only in the Pacific.
The Longspine Hatchetfish have short and deep bodies that are 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. Their dorsal fin has a toothed, pear-shaped translucent plate supported by a single spine and 9 to 11 rays.
The Longspine Hatchetfish are a bathypelagic species found at depths between 1,000 and 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. They are a poorly studied species and very little is known about their behavioral patterns.
In Mexican waters the Longspine Hatchetfish are found in all waters of both the Atlantic and the Pacific.
Due to its large transparent membrane above the anal fin, the Longspine Hatchetfish cannot be confused with any other species.
The Longspine 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.
Longspine Hatchetfish, Sternoptyx diaphana. Fish collected in a deep water trawl net off Point Loma, California, August 2010. Length: 2.3 cm (0.9 inches). Collection and identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, CA.