Wildlife Wednesdays: Deep-Sea Hatchetfish
by Olivia Maciejewski
Scientific Names: Argyropelecus, Polyipnus, and Sternoptyx
Classification:
- Kingdom: Animalia
- Class: Osteichthyes, Actinopterygii
- Family: Sternoptychidae
Population Number: Unknown
Deep-sea hatchetfish, also called marine hatchetfish, refer to many different species within a singular taxonomic family. They earn their name, “hatchetfish” from their hatchet-shaped heads. These fish have bulbous front ends, and slender tails. The most prominent features of the marine hatchetfish are their gaping, frowning mouths, in a constant state of shock and their large eyes.
Deep-sea hatchetfish eyes are big, tubular eyes that point upward, not straight. This allows them to search for prey above them. Their eyes are very sensitive to light and are therefore, very good at distinguishing shadows of their prey. Hatchetfish eyes also have the capability to focus either close up or from a distance.
In general marine hatchetfish have silver scales, unless they are the giant hatchetfish (the Argyropelecus gigas), which have brown or dark green scales. The giant hatchetfish can grow up to 4.7 to 6 inches, which is the biggest size. The smaller marine hatchetfish range from about 1 inch to 4 inches, although there are many different species of deep-sea hatchetfish, so the size varies depending on the species.
There are 45 known species of marine hatchetfish and they can be found in the Atlantic, Indian, and Pacific Oceans at extreme water depths, earning the other part of their name. Depending on the species, marine hatchetfish can be found at depths as shallow as 600 feet, to as deep as 5,000 feet, although other species can go deeper than this reaching 27,500 feet. In general, marine hatchetfish live in the midnight zone of oceans, where no sunlight from above can reach through the water.
Hatchetfish are one of the many deep-sea creatures to produce their own light. They have bioluminescent organs that line the underside of their bellies, called photophores. These organs, through the process of chemical reactions, similar to fireflies glowing, shine a pale blue light that matches the daylight filtered through to the ocean floor. This is called counterillumination and therefore hides hatchetfish well from predators from above. Marine hatchetfish can regulate the intensity and color of the light produced. Each hatchetfish species has its own particular patterns of light.
Not much is known about the deep-sea hatchetfish. Scientists are unsure of hatchetfish mating patterns as well as their life-spans, although they have come to an agreement that hatchetfish live no longer than a year. It is possible that the hatchetfish light-producing organs are related to their mating rituals, but this cannot be confirmed.
There are many other fun facts about hatchetfish. This includes their migration patterns. At nighttime, the hatchetfish swim to shallow water. This allows them to see their prey easily with their light-sensitive eyes. Now, when daylight hits, they swim back to the dark abyss of the midnight zone. Something else that is interesting is when they swim up to the shallower waters, where they can even jump out of the water to catch insects like mosquitos and flies. Hatchetfish also eat zooplankton, tiny crustaceans like seed shrimp & copepod, as well as larvae of other fish.
For more information about deep-sea hatchetfish, check out our sources:
- https://www.britannica.com/animal/hatchetfish
- http://www.seasky.org/deep-sea/hatchetfish.html
- https://www.curiousspecies.com/my-species/blog-post-title-one-yemxk-m29ek-dhngg-w852d-pr2mn-rx3pm-gm2rj-acerw-wca8h-j9yl6-3hf5w-wypyl-8jlcn-8y34a-nxk94-kwcsp-b3elp-mwfzl-b5sza-h4tab-k3k84-xce5d-hlsz8-acez5-ckd2z-2bhxf-tb47p
- https://www.montereybayaquarium.org/animals/animals-a-to-z/hatchetfish
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