These unusual deep-sea fish, found in the tropical temperate waters of the world's oceans, got their name for their bizarre characteristic appearance, reminiscent of an ax in shape - a wide body and a narrow tail.
The ax fish described in this article is most often found at depths of 200-600 meters, but has also been seen at depths of about 2000 meters.
External features of the family
Deep-sea hatchetfish or Hatchetfish (Sternoptychidae) is a family belonging to the order Stomiiformes, which includes 2 subfamilies consisting of 10 genera and 73 species. Distributed in subtropical and tropical waters of three oceans: Indian, Pacific, Atlantic. They mainly inhabit the middle layers of deep-sea areas.
The body length is from 2 to 14 centimeters. The ax fish (the photo is presented in the article) is distinguished by a very high body, strongly flattened from the sides, as well as a caudal stalk, sharply tapering towards the caudal fin.
Most varieties of this family are bright silver with a metallic bluish sheen and darker, andsometimes almost black, back. Their eyes are large, and in varieties of the genus Argyropelecus, they are also telescopic, looking up.
Description
The photo of the ax fish clearly demonstrates the originality of its shape. She has another name - wedge belly. The body of the fish, covered with silvery, easily rebounding scales, is strongly compressed from the sides. Some species have an extension of the body in the region of the anal fin. The frontal part of the dorsal fin has the shape of a blade of bones protruding from the hatchet above the muscles of the back, and the ventral part of the body has a pointed keel. Large jaws in relation to the central line of the body are at an acute angle. There is also a forked spine located at the beginning of the ventral fin. Small fat fin.
Like many other deep-sea inhabitants, hatchet fish have photophores that emit light. Unlike other fish, they use the possibility of bioluminescence (greenish light emission) for the purpose of camouflage, and not to attract prey. Photophores are located only on the belly of the fish, so their glow makes the fish invisible from below (the silhouette, as it were, dissolves against the background of sunlight penetrating into the depths of the sea). In addition, hatchets are able to adjust the intensity of the glow by controlling the brightness of the upper layers of water with their eyes.
Lifestyle
Reliably little is known about the life cycle of the ax fish, because these representatives live in hard-to-reach places. According to many researchers, their life expectancy is no more thanone year. At night, the fish is in shallow water (at a depth of about 200-300 meters), hunting for small fish and plankton. Usually she catches prey, which itself swims over it. In the daytime, they again return to a depth of 2000 meters.
Some species can congregate in large dense flocks, causing serious problems for ships using echo sounders to determine depth. Sailors first encountered such a "double bottom" in the middle of the 20th century.
Such a mass accumulation of hatchet fish attracts some species of large ocean water fish to these places. Among them are commercially valuable species, for example, tuna. In addition, hatchets make up a significant part of the diet of some other, larger inhabitants of the oceans, such as deep-sea anglerfish.
This type of fish breeds either by laying larvae that mix with plankton and sink to the depths as they mature, or by spawning.
Interesting fact
It turns out that this name (“hatchet fish”) has two types of fish that are completely unrelated. Their similarity lies in the shape of the body - both have flat and wide bodies, resembling the blade of a small ax. And they differ in their habitat - some live in the oceans, the latter are common in fresh river waters.
Freshwater fish are found in the rivers of South America and spend most of their time at the surface of the water, catching insects. They differ from other riverinhabitants not only with an unusual body shape, but also with their behavior in the process of eating, or rather, the way they eat. To catch insects, they jump out of the water, while spreading their pectoral fins in a peculiar way for maneuvering in flight.
