The mandarinfish or mandarin dragonet (Synchiropus splendidus), is a small, brightly colored member of the dragonet family, which is popular in the saltwater aquarium trade. The mandarinfish is native to the Pacific, ranging approximately from the Ryukyu Islands south to Australia.
Synchiropus splendidus is one of only two vertebrate species known to have blue colouring because of cellular pigment, the other being the closely related psychedelic mandarin (S. picturatus). The name "cyanophore" was proposed for the blue chromatophores, or pigment-containing and light-reflecting cells.
Mandarin fish are distinctive due to their unusual shape and intense coloration. They have a broad, depressed head and are primarily blue with orange, red, and yellow wavy lines. Mandarin fish are small, reaching a maximum length of 6 cm. Males are notably larger than females. Mandarin fish lack scales and instead have a thick mucus coating that has an unpleasant smell. They have 4 dorsal spines, 8 dorsal soft rays, and no anal spines. In males, the first dorsal spine is greatly elongated, sometimes long enough to reach the caudal peduncle.
Distribution and Habitat
Mandarinfish are shy and mostly passive. Normally they are found inhabiting broken coral rubble beds or under dead coral. They are so shy that any heavy breathing or movement will scare them away back to their shelters. They are usually found in groups or in pairs on reef crests and slopes in sheltered lagoons throughout much of the Western Pacific and in the Coral Triangle of biodiversity, which includes Malaysia, Indonesia, the Philippines and Australia.
Just before the sun sets, 3 to 5 females will make their way to a particular region of the reef and gather where males visit and display courtship behaviour, hoping to attract the females. The visiting males may tour around various sites in one evening spreading their sperm among a number of different females. Lucky guys J!
A successful male will then be joined by a female that will rest on his pelvic fin. The male and female mandarinfish will align themselves belly-to-belly and together, slowly rise about 1 meter above the reef. Once they are at the peak of their ascent, they will release sperm and a cloud of eggs (usually up to 200 eggs). The fish then disappear in a flash. The fertilized eggs are from that point at the mercy of the current and normally take around 18-24 hours to hatch into 1 mm long larvae. For a period of up to 2 weeks, they will remain plankton with no parental involvement before finally settling on the reef and choosing an appropriate habitat where they will live for the next 10 to 15 years.
With only a small number of active females in a group's population, competition among the males is high. In the world of mandarinfish, size does matter! The bigger and stronger males tend to be favoured by females and mate more often than smaller males. Due to the lower chances of mating, the smaller males have developed a rather desperate compensating measure. They are known to rush up to mating pairs and release sperm with the hope of random fertilization.
For any semi-serious diver, this unique mating ritual is certainly a must-watch event. It is known that mating occurs for several months each year, so there are no excuses for not having a ringside seat at this most intimate of displays.
Mandarin fish have a short incubation time and larvae that are small and develop quickly. Clutch sizes range from 12 to 205. Eggs measure from 0.7 to 0.8 mm in diameter, are colorless, spherical, and pelagic. The eggs at first are clumped together and then slowly break up into smaller units. The eyes become pigmented and the mouth becomes well developed 36 hours after fertilization. During the flexion stage, which occurs after 8 to 11 days, the caudal fins become distinctive, the pelvic fin rays move distally and the body becomes robust. The larvae are active and feeding at this stage. After 12 to 14 days, which is the settlement stage, juveniles look like the adults with a large head, and a triangular shaped body. In 18 to 21 days, the body darkens to an orange brown color with greenish banding and the dorsal spines are observed. The adult color pattern does not develop until the second month when lengths are from 10 to 15 mm. The swim bladder is retained in adults
Mandarin fish secrete mucous which might act to repel predators. The intense coloration also might play a role in avoiding predation by signalling to potential predators that they are toxic. Early development could possibly be an adaptive strategy to reduce the risk of predation. There is no available information on specific predators of the species.
Some scientist reported that the mandarinfish contains two types of secretary cells in its colourful epidermis - one that produces a thick mucus coating to protect it from the elements, and another that produces a toxin to protect it from predators. And not only is this toxic mucus coating dangerous, particularly if it makes it into a predator's open wound, but reportedly, it smells disgusting.