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Interesting Facts About Hatchetfish

Interesting Facts About Hatchetfish
The large sternal region of the body shaped like the head of a hatchet gives the hatchetfish its name. These fish come in two varieties; freshwater and marine. This article will provide some fascinating information about the hatchetfish, such as its appearance, habitat, diet, and the like.
Anuj Mudaliar
Quick Fact
Freshwater hatchetfish are easy to care for, and live as long as 5 years in captivity, if the right conditions are consistently maintained in the aquarium.

Two groups of fish, the marine stomiiformes from the family Sternoptychidae, and freshwater characins of the family Gasteropelecidae, are commonly called hatchetfish, due to their similar anatomies, characterized by a thin tail region, but a deep sternum which gives an appearance similar to a hatchet head.
Both families of hatchetfish consist of many species. The common hatchetfish, silver hatchetfish, and the marbled hatchetfish, are the most well-known varieties. Only the freshwater species can be raised in aquariums, and they are a very popular choice due to their varied color range and unique appearance. Let us now look at some interesting facts about these fascinating creatures.
Facts About Marine Hatchetfish
  • Deep sea hatchetfish consist of around 40 species, and they can be found in oceans all around the world.
  • Depending on the size and anatomy of the species, marine hatchetfish can be found in depths of 500 to 4,000 feet.
  • Most hatchetfish are very small in size, growing only to a few centimeters in length. However, a few species can grow up to a length of 6 inches.
  • Deep sea hatchetfish have a relatively short life, at the most a year.
  • Smaller species are often silver-colored, while the bigger ones may come in brown and greenish shades.
  • It is believed that marine hatchetfish use bioluminescence to attract potential mates, and after mating, the female lays a huge number of tiny eggs that float in the water.
  • Deep sea hatchetfish have flattish bodies, with cylindrical eyes that are extremely sensitive to changes in light and shadows around them. The eyes are focused upwards, which helps them see prey above them.
  • An incredible ability of these fish is to remain invisible to the eyes of predators. Hatchetfish do this by emitting light from their bodies, similar in brightness to the faint sunlight available in the deep seas.
  • The cells that emit light are called photopores, and there are a number of them all along the length of their bodies, focusing the light downwards. The light is formed due to chemical reactions occurring in the photopores.
  • Like freshwater hatchetfish, the marine variety also have large pectoral fins, which they flutter while jumping outside the water to sustain short periods of powered flight.
  • Marine hatchetfish hide in the depths of the ocean during the daytime, and come to the surface to feed at night. They eat plankton, small fish, and tiny crustaceans. They also use their ability to jump and fly to catch and eat insects that may be hovering above the water.
  • The hatchetfish has binocular vision, i.e., it can zoom in to far away objects and bring its focus back to something near, easily.

Freshwater Hatchetfish Facts
  • Freshwater hatchetfish consist of approximately 10 species, most of which are found in slow moving areas of rivers located in Central and South America. However, nowadays, these fish are being bred across the world due to their popularity in aquariums.
  • Of the marine and freshwater varieties, only the freshwater varieties can survive in aquariums. These fish are also very popular, because they don't need a lot of care, and are docile and compatible with other aquarium fish. However, the tank will usually required a lid, because of their jumping ability.
  • These fish can grow to a maximum of 3 inches, and they come in a variety of colors, such as shiny green, silver, blue, and brown.
  • They are carnivores and feed on small fish, insects, and larvae in the water.
  • The lifespan of the freshwater hatchetfish is around 3 years in the wild, and up to 5 years in captivity.
  • Of all the freshwater species, the marbled hatchet fish is considered to be the most attractive, and consequently it is the most popular species for aquarium tanks.
  • One can differentiate between male and female hatchetfish quite easily. The females almost always have a thicker body, while the males are very slender.
  • Hatchetfish are currently considered as a species of 'Least Concern' on the IUCN's Red List, so there is no fear of extinction of this fish.

Due to the depth of the marine hatchetfish habitat, scientists are yet to observe their behavior first hand, and a lot of the information on them is based on theories. The freshwater varieties however, can be a very good addition to your aquarium, which will surely dazzle you with their beauty and antics.
Crab on the coast of Sri Lanka
Marbled Hatchetfish
Closeup of a water flea floating Daphnia Pulex
Mosquito larvae and pupa