Mandarinfish

Synchiropus splendidus or Mandarinfish is a small, brightly colored bony fish. Recent molecular studies of large genetic material have identified them as Sygnathiformes, an order that includes quirky sea animals such as seahorses and pipefish. 

Mandarinfish have large, distinctive pelvic fins, which they use to ‘walk’ across the ocean floor in search of tiny invertebrates like copepods to devour. Pairs also attach their pelvic fins (hold ‘hands’) as they ascend to the surface where eggs and sperm are released. 

Mandarinfish or mandarin dragonets have many distinguishing features and interesting behaviors. In this article, we examine these psychedelic sea creatures a little closer and discover the magical world of Synchiropus splendidus. 

Appearance

Mandarinfish are a diver’s delight and a visual spectacle in the sea, and they have brilliantly bright colors, stunning patterns, and fin-flare. Their body is small and elongated, but they have broad heads, bulging red and black eyes, and pouty blue lips. 

Mandarin fish are surprisingly small, typically reaching only 6-8 centimeters (2-3 inches) in length.

These eye-catching colors include orange swirls on a bright blue body and a light blue-green face with brilliant blue stripes. The large pelvic fins are sometimes confused for the pectoral fins, which are almost transparent and propel the fish forward when swimming. 

The orange swirls change to a more striped pattern on the pelvic, anal, and caudal fins, which are rimmed with blue. The dorsal fins also have a beautiful blue and orange design. Red mandarin fish are the same species but are rarer and have red pelvic, anal, and caudal fins.  

Mandarinfish are dimorphic– females and males develop differently. Males are bigger than females and have exceptionally long spiny dorsal fins, which makes them easy to distinguish from one another.  

They often hide amongst rocks and corals, blending in with their intricate surroundings. Their slow, deliberate movements further reduce their visibility.

Habitat

Mandarinfish are saltwater fish that enjoy warm tropical waters in the western Pacific Ocean, from the Ryukyu islands to Australia (including the Philippines, Indonesia, and Hong Kong.) They inhabit inshore reefs and shallow lagoons up to depths of 1-18 m, though they generally prefer outer reef environments.  

Mandarinfishes prefer to hang around the bottom of the reef, on the sandy or silty substrate, where they use their large pelvic fins to ‘walk’ and perch on rocks and sand. They use live coral as a source of food and refuge but are not reliant on it. 

Diet

As mentioned above, mandarin fish feed on benthic (bottom-dwelling) small invertebrates like copepods and amphipods that live in shallow coral reefs and protected lagoons. 

Mandarinfish are picky eaters and likely will not eat anything other than invertebrates and small crustaceans, which makes them difficult to care for in an aquarium environment.  

Reproduction

With a maximum length of 8 cm, mandarinfish reach sexual maturity at 3 cm or 14 months. Spawning occurs in areas of the reef where small groups of males and females gather during the night. The male flashes its colors brightly and shows off its long dorsal fin to impress a mate during courtship.

Mandarinfish are pelagic spawners, and the mating pair rises to the surface at dusk to release eggs and sperm, where fertilization occurs.

During peak season, females spawn once a night or every several days and produce from 12 to 205 pelagic eggs (eggs that float on the water surface) that will hatch into larvae.

Juveniles settle on the reef together in a small area within nine days of hatching, where they stay for about a month. Researchers calculate that one generation equals about eight years, compared to a human’s, which is 20 to 30 years.  

Threats

One would think that the mandarinfish’s small size and lack of protective scales make them a perfect snack for predators, but actually, they have very few natural predators and can live for 10 or even up to 15 years. 

The fantastic patterns created by their colors, swirls, and stripes may be the first line of defense in warning hungry predators to stay away and find a meal elsewhere. They also help to camouflage the fish in the safety of coral reefs.  

These beautiful patterns make them a favorite amongst aquarists. Sadly, their popularity causes population numbers to decrease in areas like the Philippines. Humans can be considered the mandarinfish’s number one predator. 

7 more Interesting Facts about Mandarin fish

1. The first fossil record from the dragonet family dates back to the Crustaceous period (60 – 140 million years ago). 
2. They can be kept in male/female pairs in larger tanks, as they may fight with conspecifics and similar species.
3. Mandarinfish is one of only two creatures with rare blue coloration due to light-reflecting cells and blue pigmentation. The other is the picturesque mandarinfish (Synchiropus picturatus).
4. They exhibit strong site fidelity, often remaining within a small territory on the reef throughout their lives.
5. Their movements are deliberate and graceful, using their fins to “walk” along the reef rather than swim quickly.
6. Mandarinfish are non-guarding spawners, which means they do not watch over or guard their eggs.
7. Males show off their long dorsal spine and flash their colors in a dance display to attract their breeding mates.

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