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Today on Animal Fact Files we’re discussing mandarin dragonets. Also known as mandarinfish, the name "mandarin" comes from the colorful robes worn by government appointed scholars in imperial Chinese dynasties. They were called "mandarins" by non-chinese contemporary writers. The fish are also known as psychedelic fish which is another reference to their bright, beautiful colors. These colors make them popular as aquarium fish, but this is not necessarily a good thing.

Nearly all mandarin dragonets are wild caught with over 100,000 individuals removed from reefs in some years. Often, the biggest, most eye-catching individuals are collected. These individuals just happen to be the males. Mandarinfish can reach more than two and a half inches (6.3 cm) long but females are often smaller and have less pronounced dorsal fins, so they're less frequently taken. Some scientists believe this leaves the wild populations with an unbalanced ratio between the sexes, plus, females prefer to breed with bigger males!

Mandarin dragonets are shy, often hiding under rocks and in between corals in the reef. They generally stick to the seafloor but come out in the evening shortly after sunset to spawn. To initiate this process, the female snuggles up to the largest male and rests on his pelvic fin– that's the most forward positioned fin on the underside of his body. The couple swims upwards taking their mating dance above the reef, releases their gametes simultaneously, and then settles back down to the bottom in a sleeping spot with their conspecifics. The pair often appear pale after this exchange and the whole process only takes a few minutes and upwards of 200 eggs can be produced per session!

Female mandarinfish only spawn every few days, so males can be aggressive to ensure they have multiple partners each night or each week. Once they're fertilized, the eggs float, suspended in the water column, until they hatch within a day. The larvae remain pelagic for about two weeks before they've developed enough to settle to the seafloor and begin their adult lifestyle. Many of the fry are eaten by other animals during this time. It takes months for the young to reach adult size and become reproductively mature. In the wild they're believed to live a decade or longer, but their lifespan in captivity is far shorter because many die due to starvation.

Mandarin dragonets need live food. Most captive individuals won't take prepared food, so an aquarium needs to produce live food like copepods for the fish to survive. In many home aquariums, the tank doesn't produce enough food for the mandarinfish to subsist, so the fish slowly dies. On the reef, these fish eat during the day. Their bright colors give them away to watchful eyes, but mandarinfish aren't typically bothered by other animals looking for a small-sized snack. Mandarin dragonets don't have scales. They produce a smelly, bitter-tasting mucus that deters predators. It's likely their colors are a warning that they taste terrible much like the bright colors of a poison frog. This is known as aposematic signaling.

Mandarinfish live from southern Japan to northern Australian coasts in reef habitats where they have plenty of places to hide. They're not typically found more than 60 feet (18 m) below the waves. Males and females both display their fantastic, namesake colors, but males typically have larger dorsal fins– that's the fin that runs along their back. Sometimes, mandarin dragonets use their fins to "walk" along the seafloor while they forage for tiny crustaceans. It's not uncommon to see these fish living in small groups throughout the reef.

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