Description and ecology
Found in tropical, subtropical and temperate waters of the Atlantic, Pacific and Indian Oceans, marine hatchetfishes range in size from Polyipnus danae at 2.8 cm (1.1 in) to the c.12 cm (4.7 in)-long giant hatchetfish (Argyropelecus gigas). They are small deep-sea fishes which have evolved a peculiar body shape and like their relatives have bioluminescent photophores. The latter allow them to use counter-illumination to escape predators that lurk in the depths: by matching the light intensity with the light penetrating the water from above, the fish does not appear darker if seen from below. They typically occur at a few hundred meters below the surface, but their entire depth range spans from 50 to 1,500 meters deep. [1] [5]
The body is deep and laterally extremely compressed, somewhat resembling a hatchet (with the thorax being the "blade" and the caudal peduncle being the "handle"). The genus Polyipnus is rounded, the other two – in particular Sternoptyx – decidedly angular if seen from the side. Their pelvis is rotated to a vertical position. The mouth is located at the tip of the snout and directed almost straight downwards. [1]
Their scales are silvery, delicate and easily abraded. In some species, such as the highlight hatchetfish ( Sternoptyx pseudobscura ), large sections of the body at the base of the anal fin and/or caudal fin are transparent. They have perpendicular spines and blade-like pterygiophores in front of the dorsal fin. The anal fin has 11-19 rays and in some species is divided in two parts; almost all have an adipose fin. Their large, sometimes tube-shaped eyes can collect the faintest of light and focus well on objects both close and far. They are directed somewhat upwards, most conspicuously in the genus Argyropelecus . This allows them to discern the silhouettes of prey moving overhead against the slightly brighter upper waters. [1] [5]
The jellynose fishes or tadpole fishes are the small order Ateleopodiformes. This group of ray-finned fish is monotypic, containing a single family Ateleopodidae. It has about a dozen species in four genera, but these enigmatic fishes are in need of taxonomic revision.
Stomiiformes is an order of deep-sea ray-finned fishes of very diverse morphology. It includes, for example, dragonfishes, lightfishes, loosejaws, marine hatchetfishes and viperfishes. The order contains 4 families with more than 50 genera and at least 410 species. As usual for deep-sea fishes, there are few common names for species of the order, but the Stomiiformes as a whole are often called dragonfishes and allies or simply stomiiforms.
Hatchetfish may refer to three groups of fishes:
Grenadiers or rattails are generally large, brown to black gadiform marine fish of the subfamily Macrourinae, the largest subfamily of the family Macrouridae. Found at great depths from the Arctic to Antarctic, members of this subfamily are amongst the most abundant of the deep-sea fish.
The marine hatchetfishes or deep-sea hatchetfishes as well as the related bottlelights, pearlsides and constellationfishes are small deep-sea ray-finned fish of the stomiiform family Sternoptychidae. They are not closely related to and should not be confused with the freshwater hatchetfishes, which are teleosts in the characiform family Gasteropelecidae. The Sternoptychidae have 10 genera and about 70 species altogether.
Argyropelecus is an oceanic ray-finned fish genus in the deep sea hatchetfish family Sternoptychidae. A collective name is "silver hatchetfishes", but this can also refer to a species of the freshwater hatchetfishes which are not particularly closely related to this. The large pupils of these marine hatchetfishes enable them to see dim objects in the deep sea, where light barely penetrates.
Polyipnus is a genus of oceanic ray-finned fish in the family Sternoptychidae. This is the largest genus of the marine hatchetfishes subfamily Sternoptychinae and indeed of the entire Sternoptychidae. It is not quite as apomorphic as their relatives; it may be that the genus is actually a paraphyletic assemblage of less advanced Sternoptychinae and would need to be split.
Sternoptyx is an oceanic ray-finned fish genus which belongs in the family Sternoptychidae. This is the type genus of the Sternoptychidae, as well as the marine hatchetfish subfamily Sternoptychinae.
Barreleyes, also known as spook fish, are small deep-sea argentiniform fish comprising the family Opisthoproctidae found in tropical-to-temperate waters of the Atlantic, Pacific, and Indian Oceans.
The Moronidae is a family of percomorph fishes, commonly called the temperate basses, in the order Moroniformes. These fishes are found in the freshwaters of North America and the coastal waters of the North Atlantic.
The Synodontidae or lizardfishes are benthic (bottom-dwelling) marine and estuarine bony fishes that belong to the aulopiform fish order, a diverse group of marine ray-finned fish consisting of some 15 extant and several prehistoric families. They are found in tropical and subtropical marine waters throughout the world.
Argyropelecus hemigymnus, the half-naked hatchetfish, short silver hatchetfish or spurred hatchetfish, is a deep-sea hatchetfish of the genus Argyropelecus found mesopelagically in the Atlantic, Indian, and Pacific Oceans as well as in the Mediterranean Sea. It is a small species rarely exceeding 38 millimetres (1.5 in) standard length. It feeds on zooplankton, particularly ostracods and copepods. Sexual maturation occurs at length of about 22 mm, and adult males have more developed olfactory organs than females, i.e. the species is sexually dimorphic.
Argyropelecus gigas, the giant hatchetfish or greater silver hatchetfish, is a marine fish of the genus Argyropelecus. It is found in every ocean except the north Pacific in the mesopelagic zone of tropical and subtropical waters. "Giant" in relative terms only, this is the largest species of marine hatchetfishes, often exceeding 110 millimetres (4.3 in) standard length.
Argyropelecus aculeatus, the lovely hatchetfish or Atlantic silver hatchetfish, is a species of fish in the family Sternoptychidae. It may exceed 70 millimetres (2.8 in) standard length (SL). It lives in the mesopelagic zone of all oceans and performs diel vertical migration. A. aculeatus feeds on a large range of prey items; in the Gulf of Mexico ostracods and copepods dominated the diet of small individuals and euphausiids, molluscs, and fish the diet of larger ones. The silvery coloration and bioluminescence of the lovely hatchetfish allows it to hide from predators and prey in the down-welling light of the twilight zone.
Acanthurus tractus, the five-band surgeonfish, ocean surgeon, or ocean surgeonfish, is a species of ray-finned fish in the family Acanthuridae found in the western Atlantic Ocean, Florida, the Bahamas, the Caribbean Sea and the Gulf of Mexico. Until recently, it was considered a synonym of Acanthurus bahianus, but its status as a separate species was resurrected in 2011.
Argyropelecus sladeni, or Sladen's hatchetfish, is a species of ray-finned fish in the family Sternoptychidae, found in the tropical and subtropical Atlantic, Indian and Pacific Oceans. This small fish lives in the mesopelagic zone by day and makes a daily vertical migration to the epipelagic zone at night.
Sternoptyx diaphana, the diaphanous hatchetfish, is a species of deep sea ray-finned fish in the family Sternoptychidae. It is the type species of the genus Sternoptyx, and was first described by the French naturalist Johann Hermann in Der Naturforscher 1781.
Polyipnus clarus, commonly known as the stareye hatchetfish or slope hatchetfish, is a species of ray-finned fish in the family Sternoptychidae. It occurs in deep water in the western Atlantic Ocean from the Gulf of Maine southward to the Caribbean Sea and the Gulf of Mexico. It most commonly occurs between 300 and 400 metres but can range from 40 and 830 metres.
Polyipnus spinosus, commonly known as the spiny hatchetfish, is a species of ray-finned fish in the family Sternoptychidae. It occurs in deep water in the western central Pacific Ocean, at depths down to about 500 metres (1,600 ft).
Argyropelecus olfersii is a common species of marine hatchetfish, found in mesopelagic waters.
