Dragonets are small, percomorph, marine

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

of the diverse family Callionymidae (from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''kallis'', "beautiful" and ', "name") found mainly in the tropical waters of the western Indo-Pacific. They are benthic organisms, spending most of their time near the sandy bottoms, at a depth of roughly two hundred meters. There exist 139

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 ...

of the fish, in nineteen genera. Due to similarities in

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

and behavior, dragonets are sometimes confused with members of the

goby Goby is a common name for many species of small to medium sized ray-finned fish, normally with large heads and tapered bodies, which are found in marine, brackish and freshwater environments. Traditionally most of the species called gobies have b ...

family. However, male dragonets can be differentiated from the goby by their very long dorsal fins, and females by their protruding lower jaws. The

Draconettidae The Draconettidae, slope dragonets, are a small family (about 14 species) of fish in the order Perciformes. They are found in temperate to tropical waters of the Atlantic, Indian and western Pacific Oceans. They are closely related to, and appea ...

may be considered a sister family, whose members are very much alike, though rarely seen.

Genera

The following genera are classified within the Callionymidae: * '' Anaora''

J. E. Gray John Edward Gray, Fellow of the Royal Society, FRS (12 February 1800 – 7 March 1875) was a British zoology, zoologist. He was the elder brother of zoologist George Robert Gray and son of the pharmacologist and botanist Samuel Frederick Gray ...

, 1835 * '' Bathycallionymus'' Nakabo, 1982 * '' Callionymus''

Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

, 1758 (including ''

Calliurichthys ''Calliurichthys'' is a subgenus of ''Callionymus'', a genus dragonets, native to the western Pacific Ocean. Some authorities consider it to be a valid genus. Species There are currently two recognized species in this subgenus: * '' Callionymus ...

'') * ''

Diplogrammus ''Diplogrammus'' is a genus of dragonets. Species There are currently 8 recognized species in this genus: * ''Diplogrammus goramensis'' ( Bleeker, 1858) (Goram dragonet) * ''Diplogrammus gruveli'' J. L. B. Smith, 1963 (Gruvel's dragonet) * ''Di ...

Gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

, 1865 (including ''Chalinops'') * ''

Draculo ''Draculo'' is a genus of dragonets found mainly in the tropical waters of the western Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asi ...

'' Snyder, 1911 * ''

Eleutherochir ''Eleutherochir'' is a monotypic genus of dragonets native to the Indian Ocean and the western Pacific Ocean. It contains a single species, ''Eleutherochir opercularis'', the flap-gilled dragonet which is distributed from Sri Lanka and the east c ...

'' Bleeker, 1879 * '' Eocallionymus'' Nakabo, 1982 * ''

Foetorepus ''Foetorepus'' is a genus of dragonets. The validity of this genus has been questioned with some experts regarding it as a junior synonym of Synchiropus. Species There are currently 11 recognized species in this genus: * '' Foetorepus agassizi ...

'' Whitley, 1931 * ''

Neosynchiropus ''Neosynchiropus'' is a small genus of Indo-Pacific dragonets. This genus is considered by some authorities to be a synonym of '' Synchiropus''. Species There are three species classified as being members of the genus ''Neosynchiropus'': * '' Ne ...

'' Nalbant, 1979 * '' Paracallionymus''

Barnard Barnard is a version of the surname Bernard, which is a French and West Germanic masculine given name and surname. The surname means as tough as a bear, Bar(Bear)+nard/hard(hardy/tough) __NOTOC__ People Some of the people bearing the surname Ba ...

, 1927 * '' Protogrammus'' Fricke, 1985 * '' Pseudocalliurichthys'' Nakabo, 1982 * '' Repomucenus'' Whitley, 1931 * '' Spinicapitichthys'' Fricke, 1980 * ''

Synchiropus ''Synchiropus'' is a genus of fish in the family Callionymidae found mainly in the tropical waters of the Indo-Pacific region. Species There are currently 44 recognized species in this genus: * '' Synchiropus atrilabiatus'' (Garman, 1899) (Ant ...

'' Gill, 1859 * '' Tonlesapia'' Motomura & Mukai, 2006

Description

These "little dragons" are generally very colorful and possess cryptic patterns. Their bodies are elongated and scaleless. A large preopercular spine is characteristic of this fish, and has been reported to be

venomous Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...

in some species. All fins are large, showy and elongated; the first high dorsal fin usually has four spines; in males, the first of these spines may be further adorned with filamentous extensions. Dragonets have flattened, triangular heads with large mouths and eyes; their tail fins are fan-shaped and tapered. The largest species, the longtail dragonet (''Callionymus gardineri'') reaches a length of . At the other end of the spectrum, the Saint Helena dragonet (''Callionymus sanctaehelenae'') reaches a length of just . Many species exhibit marked

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

: males and females are coloured and patterned differently from each other, and (in addition to the spine filament) males have a much higher dorsal fin. This difference is extreme in the high-finned dragonet (''Synchiropus rameus'').

Reproduction

Dragonet

spawning Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquat ...

occurs during late afternoons, right before the sun sets. The fish's spawning behavior is divided into four distinctive stages:

courtship display A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...

, pairing, ascending, and the release of eggs and

milt Milt is the seminal fluid of fish, mollusks, and certain other water-dwelling animals which reproduce by spraying this fluid, which contains the sperm, onto roe (fish eggs). It can also refer to the sperm sacs or testes that contain the seme ...

. Both male and female dragonets have been observed displaying and courting each other, although the practice is much more frequent in the males. Females only do so when they are ready to spawn and are in need of a mate. Both sexes display by spreading their

pectoral Pectoral may refer to: * The chest region and anything relating to it. * Pectoral cross, a cross worn on the chest * a decorative, usually jeweled version of a gorget * Pectoral (Ancient Egypt), a type of jewelry worn in ancient Egypt * Pectorali ...

and caudal fins, and moving around or by the side of the other sex. Males will sometimes also spread their

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

fins, repeatedly open and close their mouths, and position themselves on top of the females and rub their abdomens with their bodies. If a female accepts a male for spawning, they form a pair. Occasionally, another male might intrude upon the pair as they are mating and attempt to sneak fertilizations with the female. Such an act would result in aggression by the original male. Prior to spawning, a male and female dragonet pair will ascend approximately 0.7-1.2 meters up a

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

from the sand at the bottom of the ocean. The male assumes a parallel position to the female, touching the female's side with the part of its body near its

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

fin. The pair rises slowly up the water column, moving in a semicircular manner by swimming with their pectoral fins. The ascent occurs in two phases. During the first phase, the dragonet pair moves upward about fifteen centimeters and rests for around five seconds. Then it proceeds with its second rise. During this second phase of the ascent, the male and female flex their bodies and move their

genital papilla The genital papilla is an anatomical feature of the external genitalia of some animals. In mammals In mammals, the genital papilla is a part of female external genitalia not present in humans, which appears as a small, fleshy flab of tissue. The p ...

e toward each other. The male releases its ejaculate and the female releases its eggs. The release of eggs occurs singly and continuously for approximately five seconds. The eggs are

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

, floating freely in the water column. The female releases a high number of eggs during each spawning, and the dragonets do not guard their offspring. The eggs are buoyant, so they intermingle with plankton and get swept away by the ocean current. After the spawning, the dragonet pair parts from each other and swims back down to the ocean floor. Male dragonets are polygynous, and will begin to search for other females to repeat the mating process with. They generally spawn with several different females within one reproductive day. Dragonets are very sexually dimorphic, with the males being much larger and having longer fins than the females. This

may have evolved in males in response to female mate choice, male-male competition, or both.

Competition/aggression

Male dragonets form dominance hierarchies and act extremely aggressively towards each other. They are often observed chasing and biting, which occurs primarily when two males are close to a female during courtship and pairing. Fights can be very intense; when one male recognizes another male near its breeding site, it will rush toward it and bite at its rival's mouth. The two may bite at each other and twist their bodies around one another for longer than a minute. As a result of this behavior, male dragonets suffer higher mortality rates than females do after attaining maturation. The highest mortality rates in adult males occur during breeding. Males have evolved larger bodies, as well as longer spines and rays, in order to achieve dominance in reproduction. They have also developed bright colors so as to more effectively compete for female attention. These

secondary sex characteristics Secondary sex characteristics are features that appear during puberty in humans, and at sexual maturity in other animals. These characteristics are particularly evident in the sexually dimorphic phenotypic traits that distinguish the sexes of a s ...

further reduce the survival potential of male dragonets, as they increase the risk of predation, require greater energy costs, and escalate the risk of suffering injuries.

Feeding

Feeding by the dragonet occurs throughout the day, including the intervals between courtships and spawning. The fish feeds entirely on benthic sources, primarily copepods,

amphipods Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far describ ...

, and other small

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...

living on blades of sea grass. Species of dragonets from different locations show variations in specific food preference, attributable to the different availabilities and abundances of food organisms in those places. All of them feed by extending their highly protractible jaws toward their food and drawing it into the mouths, frequently followed by the expulsion of sand. No evidence suggests that dragonets are territorial. Individuals do not defend specific areas of substrate, as well as any resources that might be present on them, from intrusion by conspecifics or other fish species. Among ''Calliurichthys japonicus'' and ''Repomucenus huguenini'', the two most abundant dragonet species, amphipods are the most plentiful prey during the spring and winter months. The fish also supplement their diets with

polychaetes Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made ...

, bivalves, and

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...

in these periods. During the summer, the dragonets feed primarily on ophiuroids and amphipods. In this season, ophiuroids are the most dominant in number. Finally, in the fall, the two species predominantly consume polychaetes, amphipods, and

, with polychaetes contributing the highest amount.

Locomotion

Four types of swimming are observed in the dragonet. The first is burst swimming, the most common of the four, and utilized during

foraging Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavi ...

. The dragonet uses its pelvic fins to propel its body off of a substrate, and then its pectoral fins to guide itself forward. The second is continuous swimming, often utilized by males when approaching a potential mate or retreating during an aggressive encounter with another male. The dragonet uses its pectoral fins to propel its body forward, and its pelvic fins to lift and guide itself. The third type of swimming is rapid swimming, which is observed when the dragonet is attacking or fleeing. The fish primarily uses its caudal fins to achieve a quick speed. Finally, the fourth type is vertical swimming, utilized by the dragonet during spawning when it ascends. The pectoral fins are used to propel the fish's body up the water column.

Defense

In defense against its predators, the dragonet rapidly buries itself under the sand at the bottom of the ocean so that only its eyes remain visible. Many species of the fish also are capable of producing and secreting foul-tasting and -smelling substances that may ward off any potential predators.

Timeline

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Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

from: -55.8 till: -33.9 color:eocene text:

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

from: -33.9 till: -23.03 color:oligocene text: Oligocene from: -23.03 till: -5.332 color:miocene text:

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

from: -5.332 till: -2.588 color:pliocene text: Plio. from: -2.588 till: -0.0117 color:pleistocene text:

Pleist. The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

from: -0.0117 till: 0 color:holocene text: H. bar:eratop from: -65.5 till: -23.03 color:paleogene text: Paleogene from: -23.03 till: -2.588 color:neogene text: Neogene from: -2.588 till: 0 color:quaternary text: Q. PlotData= align:left fontsize:M mark:(line,white) width:5 anchor:till align:left color:eocene bar:NAM1 from: -55.8 till: 0 text: Callionymus PlotData= align:center textcolor:black fontsize:M mark:(line,black) width:25 bar:period from: -65.5 till: -55.8 color:paleocene text: