Synchiropus splendidus is a beautiful fish better known as the mandarinfish, mandarin dragonet or mandarin goby. The mandarinfish is not actually a goby though, they are just superficially similar to the members of the Gobiidae, and are actually in the Callionymidae, the dragonet family. The Callionymidae and the mandarinfish are native to the western Pacific. Mandarins can be found in shallow reefs and sheltered lagoons, where they lead a benthic lifestyle. Using their large pelvic fins they “walk” along the seafloor and reef looking for food.
The blue colouration of the mandarinfish is unique (except for the closely related Synchiropus picturatus) because it is the result of cellular pigment. Blue colouration in other vertebrate species is structural, meaning that their skin, scales or feathers interact with light in such a way on a microscopic level that they are able to reflect certain wavelengths of light back without having a pigment for that colour. The vivid colours on the train feathers of the peacock are a great example of structural colouration.
Instead of scales, mandarinfish have a layer of slime covering and protecting their body; this slime is smelly and has a bitter taste. The bright colouration of the fish acts as a warning signal to potential predators that they don’t taste very good and wouldn’t make a good meal. Signals, colouration in this case, that warn predators of an organism’s defenses are called aposematic signals and can be found all throughout the animal kingdom in both vertebrates and invertebrates. Some species have even evolved to mimic the colours of dangerous species, like the harmless milk snake having very similar colouration to the highly venomous coral snake. This is called Batesian mimicry.
Mandarins are considered difficult to keep in captivity because of their specific feeding habits. In the wild they will continuously feed during the day, pecking at prey found on the substrate in their territory, which consists mainly of copepods. This combination of factors can prove to be tough for people caring for these fish as some never accept frozen or flake food and subsequently starve. By seeding your tank with copepods you’ll be able to better emulate a natural reef environment and provide your mandarinfishes with a proper diet as they are able to graze throughout the day on their natural prey.
Sadovy, Y., Mitcheson, G., Rasotto, M.B., 2001. Early development of the mandarinfish Synchiropus splendidus (Callionymidae), with notes on its fishery and potential for culture.Aquarium Sciences and Conservation. 3:253-263