Dragonets are small, perciform, marine fish of the diverse family Callionymidae, found mainly in the tropical waters of the western Indo-Pacific. They are often miscategorised as gobies or blennies by fish sellers for similar morphology and behaviour.
These “little dragons” are generally very colourful with cryptic patterns and hence could be perfect for your reef tank. Their bodies are elongated and scaleless. A large preopercular spine is characteristic of this group. Some species has been reported to be venomous. All fins are large, showy and elongated.
The first high dorsal fin usually has four spines. Males further have filamentous extensions on the first of these spines. Dragonets have flattened triangular heads with large mouths and eyes, which give them a dragon-like look. Their tail fins are fan-shaped and tapered.
The largest species, the long-tail dragonet (Callionymus gardineri) reaches a length of 30 centimetres (12 in). At the other end of the scale, the Saint Helena dragonet (Callionymus sanctaehelenae) reaches a length of just 2 centimetres (0.79 in).
Many species exhibit marked sexual dimorphism in which males and females are coloured and patterned differently, and (in addition to the spine filament) males have a much higher dorsal fin. This theme is taken to extremes in the high-finned dragonet (Synchiropus rameus).
Dragonets are benthic and generally live at the bottom of the sea and constantly hunt tiny invertebrates for food. Dragonets feed mostly on crustaceans, worms and other small invertebrates rooted out from the substrate. The dragonet’s large pectoral fins serve as a primary means of propulsion.
Although their bright colours and showy fins make them a popular choice for the aquarium, most dragonets are picky eaters and will only accept live food like copepods and amphipods, making them difficult to keep in captivity. They do not readily accept prepared foods and often starve soon after purchase unless you provide a refugium or place for the invertebrates to reproduce safely without any fish being able to reach them. So, larger tanks are desired because they can support a larger population of the copepods and amphipods. They prefer sandy or rocky substrates, sometimes near reefs, to find enough food.
They are considered to be reef safe and do best in reef aquariums of 55 gallons or larger with large amounts of live rock.
Spawning involves elaborate courtship displays. The males show off their flashy fins and repeatedly open and close their mouths. If the female is interested, pairing occurs and the two fish rise upwards, with male supporting the female on its pectoral fins. Eggs and sperm are released in mid-water, where fertilization takes place. The buoyant eggs subsequently become part of the plankton, drifting with the currents until hatching.
The most common commercially available dragonets are:
Mandarinfish (Synchiropus splendidus)
It is a brightly colored member of the dragonet family. It is difficult to keep in an aquarium but if you really want this stunner, go for refugium in the tank. It can grow up to 6 cm (2.4 in).
Ocellated dragonet or scooter blenny (Synchiropus ocellatus)
Though not a true blenny, it is also known as Scooter Blenny. The care level is moderate but you have to attach a refugium in your aquarium. It grows up to a size of 8 cm (3.1 in).
Spotted mandarin (Synchiropus picturatus)
As the name suggests, it has spots all over. Even it is difficult to keep in a reef tank. As usual, you have to use a refugium in your aquarium. They grow up to a size of 10 cm (3.9 in).
Other varieties of dragonets that you can keep in a reef tank are Psychedelic mandarin dragonet (Synchiropus picturatus) and the Starry dragonet (Synchiropus stellatus) or Red Scooter Blenny, though not a true blenny. Starry dragonets grow up to 12 cm (4.7 in).