Dragonets are small percomorph marine fish of the diverse family Callionymidae (from the Greek 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 of the fish, in nineteen genera.

Due to similarities in morphology and behavior, dragonets are sometimes confused with members of the goby 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 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 <small>J. E. Gray, 1835</small>
  • Bathycallionymus <small>Nakabo, 1982</small>
  • Callionymus <small>Linnaeus, 1758</small> (including Calliurichthys)
  • Diplogrammus <small>Gill, 1865</small> (including Chalinops)
  • Draculo <small>Snyder, 1911</small>
  • Eleutherochir <small>Bleeker, 1879</small>
  • Eocallionymus <small>Nakabo, 1982</small>
  • Foetorepus <small>Whitley, 1931</small>
  • Neosynchiropus <small>Nalbant, 1979</small>
  • Paracallionymus <small>Barnard, 1927</small>
  • Protogrammus <small>Fricke, 1985</small>
  • Pseudocalliurichthys <small>Nakabo, 1982</small>
  • Repomucenus <small>Whitley, 1931</small>
  • Spinicapitichthys <small>Fricke, 1980</small>
  • Synchiropus <small>Gill, 1859</small>
  • Tonlesapia <small>Motomura & Mukai, 2006</small>

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, The fish's spawning behavior is divided into four distinctive stages: courtship display, pairing, ascending, and the release of eggs and milt. Both sexes display by spreading their pectoral and caudal fins, and moving around or by the side of the other sex. Males will sometimes also spread their dorsal 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 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 fin. This sexual dimorphism may have evolved in males in response to female mate choice, male-male competition, or both. 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 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. 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.

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. 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.

Timeline

<timeline>

ImageSize = width:1000px height:auto barincrement:15px

PlotArea = left:10px bottom:50px top:10px right:10px

Period = from:-65.5 till:10

TimeAxis = orientation:horizontal

ScaleMajor = unit:year increment:5 start:-65.5

ScaleMinor = unit:year increment:1 start:-65.5

TimeAxis = orientation:hor

AlignBars = justify

Colors =

  1. legends

id:CAR value:claret

id:ANK value:rgb(0.4,0.3,0.196)

id:HER value:teal

id:HAD value:green

id:OMN value:blue

id:black value:black

id:white value:white

id:cenozoic value:rgb(0.54,0.54,0.258)

id:paleogene value:rgb(0.99,0.6,0.32)

id:paleocene value:rgb(0.99,0.65,0.37)

id:eocene value:rgb(0.99,0.71,0.42)

id:oligocene value:rgb(0.99,0.75,0.48)

id:neogene value:rgb(0.999999,0.9,0.1)

id:miocene value:rgb(0.999999,0.999999,0)

id:pliocene value:rgb(0.97,0.98,0.68)

id:quaternary value:rgb(0.98,0.98,0.5)

id:pleistocene value:rgb(0.999999,0.95,0.68)

id:holocene value:rgb(0.999,0.95,0.88)

BarData=

bar:eratop

bar:space

bar:periodtop

bar:space

bar:NAM1

bar:space

bar:period

bar:space

bar:era

PlotData=

align:center textcolor:black fontsize:M mark:(line,black) width:25

shift:(7,-4)

bar:periodtop

from: -65.5 till: -55.8 color:paleocene text:Paleocene

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

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

from: -23.03 till: -5.332 color:miocene text:Miocene

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

from: -2.588 till: -0.0117 color:pleistocene text:Pleist.

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:Paleocene

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

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

from: -23.03 till: -5.332 color:miocene text:Miocene

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

from: -2.588 till: -0.0117 color:pleistocene text:Pleist.

from: -0.0117 till: 0 color:holocene text:H.

bar:era

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.

</timeline>

See also

  • List of fish common names
  • List of fish families

References

  • Smith, J.B.L. 1963. Fishes of the families Draconettidae and Callionymidae from the Red Sea and the Western Indian Ocean. Ichthyological Bulletin; No. 28. Department of Ichthyology, Rhodes University, Grahamstown, South Africa