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Lanternfish

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Lanternfish are small, mesopelagic fish belonging to the family Myctophidae. They are found in oceans across the entire globe. These fish are named for their conspicuous use of bioluminescence, which is the ability to produce their own light. There are 246 known species within 33 different genera. They are among the most diverse and populous vertebrates on Earth. Some estimates suggest their total global biomass is between 1.8 and 16 gigatonnes. This accounts for up to 65% of all deep-sea fish biomass.

Lanternfishes of the family Myctophidae
Lanternfishes of the family Myctophidae

The bodies of lanternfish are typically slender and compressed. They are covered in small, silvery, deciduous cycloid scales. Most species possess a large, rounded head and large eyes. Their mouths are large and terminal, with jaws held closely together. Rows of small teeth line these jaws. Most lanternfish also have a gas bladder, which helps them control buoyancy. However, in a few species, this bladder degenerates or fills with lipids as they mature.

Lobianchia dofleini1
Lobianchia dofleini1

A defining feature of these fish is the presence of photophores. Photophores are specialized light-producing organs. In almost all species, these organs appear in paired, ventrolateral rows on the head and body. They emit a weak light that can be blue, green, or yellow. These light patterns are often species-specific. In some cases, the patterns even differ between males and females. For example, in some species, males have luminous caudal patches above the tail, while females have them below. Some species even have specialized photophores near their eyes that act like headlights.

Lobianchia dofleini1
Lobianchia dofleini1

Lanternfish use their light for a survival strategy called counterillumination. They use the photophores on their bellies to camouflage their silhouette. When viewed from below, predators might normally see a dark shape against the light from above. To prevent this, lanternfish regulate the brightness of their blue light. They match the ambient light level coming from the surface. This effectively masks their shape from hungry predators. This behavior is a key part of their complex ecology.

Lobianchia dofleini1
Lobianchia dofleini1

Many lanternfish species participate in diel vertical migration. This is a daily movement pattern driven by light and food. During daylight hours, they stay in the dark mesopelagic zone. As sundown approaches, they rise into the shallower epipelagic zone. They do this to feed on zooplankton. They also do this to avoid predators that hunt in the light. After feeding at the surface, they descend back to the lightless depths before daybreak. This movement is vital for the ocean's biological pump. By releasing fecal pellets at great depths, they help move carbon through the water column.

The history of lanternfish can be traced through the fossil record. The earliest known fossil lanternfish is †Garganomyctophum from the Santonian of Italy. Scientists study their history using otoliths, which are small ear stones found in fish. In the early Oligocene, lanternfish transitioned from coastal areas to the deep ocean. This change happened as ocean circulation shifted to a thermohaline regime. This regime involved the cooling of deep water and changes in nutrient supplies. During the late Miocene, a "biogenic bloom" occurred. This period saw an increase in lanternfish diversity and size, which happened alongside the rise of baleen whales.

Because they are so numerous, lanternfish are a critical link in the marine food chain. They are heavily preyed upon by many animals. These include whales, dolphins, sharks, tuna, and salmon. Even seabirds like penguins and large squid like the jumbo squid eat them. Their massive numbers even affect human technology. During World War II, sonar operators were puzzled by a "false ocean bottom." They saw a signal 300 to 500 meters deep that moved with the light. This was actually the deep scattering layer. This layer is formed by millions of fish swimbladders reflecting sonar waves.

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Lanternfishes of the family Myctophidae.webp
File:Lobianchia dofleini1.jpg
Lobianchia dofleini1.jpg
File:Population of the deep-sea Myctophidae and other groups.png
Population of the deep-sea Myctophidae...
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