The Gonostomatidae are a family of

mesopelagic The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...

marine fish, commonly named bristlemouths, lightfishes, or anglemouths. It is a relatively small

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

, containing only eight known

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

and 32

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. However, bristlemouths make up for their lack of diversity with relative abundance, numbering in the hundreds of trillions to

quadrillion Two naming scales for large numbers have been used in English and other European languages since the early modern era: the long and short scales. Most English variants use the short scale today, but the long scale remains dominant in many non-Eng ...

s. The genera ''

Cyclothone ''Cyclothone'' is a genus containing 13 extant species of bioluminescent fish, commonly known as 'bristlemouths' or 'bristlefishes' due to their shared characteristic of sharp, bristle-like teeth. These fishes typically grow to around 1-3 inche ...

'' (with 13 species) is thought to be one of the most abundant vertebrate genera in the world. The fossil record of this family dates back to the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

. Living bristlemouths were discovered by

William Beebe Charles William Beebe ( ; July 29, 1877 – June 4, 1962) was an American naturalist, ornithologist, marine biologist, entomologist, explorer, and author. He is remembered for the numerous expeditions he conducted for the New York Zoological S ...

in the early 1930s and described by L. S. Berg in 1958. The fish are mostly found in the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...

Indian Indian or Indians may refer to: Peoples South Asia * Indian people, people of Indian nationality, or people who have an Indian ancestor ** Non-resident Indian, a citizen of India who has temporarily emigrated to another country * South Asia ...

, and

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

s, although the species ''

Cyclothone microdon ''Cyclothone'' is a genus containing 13 extant species of bioluminescent fish, commonly known as 'bristlemouths' or 'bristlefishes' due to their shared characteristic of sharp, bristle-like teeth. These fishes typically grow to around 1-3 inche ...

'' may be found in

Arctic The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...

waters. They have elongated bodies from in length. They have a number of green or red light-producing

photophore A photophore is a glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors, ...

s aligned along the undersides of their heads or bodies. Their chief common name, bristlemouth, comes from their odd, equally sized, and bristle-like teeth. They are typically black in color which provides camouflage from predators in deep, dark waters. They mainly feed on zooplankton and small crustaceans due to their small size.

Morphology

Bristlemouths are

protandrous Sequential hermaphroditism (called dichogamy in botany) is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, ...

, therefore a male first hermaphrodite. They begin their lives as males and some of them switch to female. Male bristlemouths are smaller than females. Bristlemouths have large jaws that are capable of catching prey larger than themselves. The length of the S. glarisianus's (a species of Bristlemouth) lower jaw is equaled to 70% of the entire length of their head. The lower jaw of the Bristlemouths is not functional in terms of masticating their prey. It is therefore hypothesized that they swallow their prey tail first. Bristlemouths are extremely small, measuring on average 75 mm. Bristlemouths have elongated bodies, small eyes, short snouts, large mouths, and large jaws. The position of the dorsal fin begins in line with the anal fin. The difference between bristlemouths species is found in the intensity of their pigmentation and

size. For the majority of the species, the morphology remains the same. Bristlemouths are mostly dark in pigmentation but at times can display translucently. Bristlemouths contain a pineal organ which functions to detect slow changing ambient light. This allows the Bristlemouth to have control over its circadian clock and seasonal behavior. Due to the small size of the fish, they are easy prey to dragonfish and

fangtooth Fangtooths are beryciform fish of the family (biology), family Anoplogastridae (sometimes spelled "Anoplogasteridae") that live in the deep sea. The name is from the Greek language, Greek , meaning "unarmed", and (), meaning "stomach". With a ci ...

Taxonomy

Some classifications include the genera '' Pollichthys'' and ''

Vinciguerria ''Vinciguerria'' is a genus of lightfishes, family Phosichthyidae. It is named for Dr. Decio Vinciguerra (1856–1934), an Italian ichthyologist. Included species There are currently five extant species recognized in this genus: * '' Vinciguerri ...

'', but this article follows

FishBase FishBase is a global species database of fish species (specifically finfish). It is the largest and most extensively accessed online database on adult finfish on the web.

in placing them in the family

Phosichthyidae Lightfishes are small stomiiform fishes in the family Phosichthyidae The earliest fossils of lightfishes are from Oligocene-aged Paratethyan marine strata in the Czech Republic. They are very small fishes found in oceans throughout the world: ...

. Some classifications include species in the genus ''Zaphotias'', but these are junior synonyms of the species ''Bonapartia pedaliota''.

Feeding habits

Brislemouths feed mostly on

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

and small

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s. Their diet is composed of a range from 92-98% of Crustacea. A minor part of their diet is made up of opportunistic encounters with smaller fish. Brislemouths that consume fish prey are found in individuals ranging from 70 mm to 75 mm. Bristlemouths do not have seasonal trends when it comes to their feeding habits. Bristlemouths are diel vertical migrators, therefore migrating closer to the surface waters in the nighttime in order to find more food. Out of the thirteen bristlemouth species, eight have been found near the surface therefore explaining their DVM behaviors. Bristlemouths are able to efficiently capture their prey due to their bioluminescent nature.

Bioluminescence

Bristlemouths are light emitting fish. Bristlemouths rely on their

bioluminescence Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some b ...

for different outcomes. Some rely on it to find prey while others use it to avoid predation. However, the most common way that their bioluminescence is used is to signal between fish in the same way people "dance or wear bright colors at the nightclub."

References

* {{Taxonbar, from=Q796557 Extant Miocene first appearances Ray-finned fish families