Dragonets are small, percomorph, marine fish of the diverse family Callionymidae (from the Greek kallis, "beautiful" and onyma, "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.
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,[1] and has been reported to be venomous 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 30 centimetres (12 in). At the other end of the spectrum, the Saint Helena dragonet (Callionymus sanctaehelenae) reaches a length of just 2 centimetres (0.79 in). Many species exhibit marked sexual dimorphism: 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).
Dragonet spawning occurs during late afternoons, right before the sun sets.[2] The fish's spawning behavior is divided into four distinctive stages: courtship display, pairing, ascending, and the release of eggs and milt.[2] 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.[3] 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.[4]