Animal
Mandarinfish
The mandarinfish is a tiny reef fish with wavy blue and orange stripes. It creeps along the bottom of the reef. At sunset, pairs dance up toward the surface.
The mandarinfish is a small, shy fish from the coral reefs of the western Pacific Ocean. It has no scales; instead its skin is covered with slimy mucus and painted with swirling blue, orange and green lines. It hops along the reef bottom on fan-shaped fins, picking up tiny animals, and at dusk males and females rise together to release their eggs.
Synchiropus splendidus is a dragonet (family Callionymidae), a ray-finned fish of shallow western Pacific reefs. It is scaleless, with a smelly, bitter-tasting mucus coat, and grows to only about 6 to 9 centimeters. Pairs spawn at dusk, releasing floating eggs. The IUCN lists it as Least Concern (2019) but notes heavy collection for the aquarium trade and local declines in the Philippines.
Photo: I, Luc Viatour, CC BY-SA 3.0, via Wikimedia Commons
Meet the mandarinfish
The mandarinfish is a very small fish.
It has blue, orange and green wavy lines all over. Its fins have bright blue edges. It lives on coral reefs in warm sea.
The mandarinfish is one of the most colorful fish on a coral reef. Its body is orange with curving green or blue stripes outlined in black, and its fins are edged with deep blue. It has a broad, flat head and big eyes.
It is tiny. Even the biggest mandarinfish are only about 9 centimeters long, shorter than a grown-up's hand. It belongs to a family of small bottom-living fish called dragonets.
Synchiropus splendidus is a ray-finned fish (class Actinopterygii) in the dragonet family, Callionymidae. Animal Diversity Web describes a broad, depressed head and a mostly blue body with wavy orange, red and yellow lines; FishBase notes that rare individuals have a bright red base color.
Sources differ on size: the IUCN gives a maximum total length of 9 centimeters, FishBase 7 and Animal Diversity Web 6. Males are notably larger than females, and the male's first dorsal spine is much longer. The dorsal fins carry 4 spines and 8 soft rays (FishBase).
Quick facts
- Group
- Fish
- Length
- up to 9 cm
- Lifespan in the wild
- 10 to 15 years
Shallow reefs of the western Pacific
Mandarinfish live in warm, shallow sea.
They stay near the bottom of coral reefs. They hide among corals and broken bits of coral.
Mandarinfish live in the tropical western Pacific Ocean, from the Ryukyu Islands of southern Japan to the Philippines, Indonesia, northeastern Australia, Papua New Guinea, Vanuatu and New Caledonia.
They live in shallow water, from the surface down to about 18 meters. They stay right on the reef bottom, on sand or silt among corals, rocks and coral rubble, and often hide among live coral branches.
The IUCN describes a tropical western Pacific range from the Ryukyu Islands to the Philippines, Micronesia, Indonesia, Queensland in Australia, and Papua New Guinea to Vanuatu and New Caledonia; it possibly also occurs in the Andaman and Nicobar Islands. Depth is 0 to 18 meters.
It is a cryptic, demersal species that perches on rocks and sand over sandy or silty bottoms, seems to prefer outer reefs, and uses branching Porites corals, rubble and silted areas. It is often found with live coral for food and shelter but does not depend on it entirely (IUCN). FishBase adds protected lagoons and inshore reefs, usually in small groups spread over a small area.
Its habitat
Where can you find this animal?
- Lives here naturally · Countries and seas named by a scientific source
- Sightings recorded · Records of wild sightings (GBIF)
Lives here naturally · Countries and seas named by a scientific source
Shallow coral reefs of the tropical western Pacific, from Japan's Ryukyu Islands to the Philippines, Indonesia, Queensland, Papua New Guinea, Vanuatu and New Caledonia. The fish lives only on reefs along the coasts of each place shown. The IUCN also lists Micronesia, Palau and Singapore (too small to shade on this map) and a possible presence in India's Andaman and Nicobar Islands.
Places: Australia, Brunei, Indonesia, Japan, Malaysia, New Caledonia, Papua New Guinea, Philippines and 3 more places.
Source: iucn-red-list · checked October 2026
Sightings recorded · Records of wild sightings (GBIF)
Counts of GBIF records of wild observations (human and machine) and preserved specimens. Records include introduced populations, vagrants, escaped or released animals and misidentifications, so a country with records is not necessarily part of the native range.
Wild sightings have been recorded in Indonesia, Philippines, Japan, Malaysia, Australia, New Caledonia, Papua New Guinea, Solomon Is. and 9 more places.
Source: gbif · checked October 2026
Range maps show where scientists say an animal lives, often country by country. An animal may live in only part of a country shown, and sightings records can include animals that wandered far from home.
Tiny food from the reef floor
Mandarinfish eat very tiny animals.
They find them on rocks and sand on the reef floor.
Mandarinfish feed on the bottom. They eat very small animals that live on the reef and among rocks: tiny crustaceans (relatives of shrimp), small worms and even single-celled creatures.
Because they need so much live, tiny food, they are hard to keep in aquariums. Animal Diversity Web notes that wild mandarinfish can live 10 to 15 years, but in captivity they usually live only 2 to 4 years.
Animal Diversity Web lists small benthic crustaceans such as amphipods and isopods, small worms and protozoans, mostly found living on reef rock.
This diet is why the species does poorly in captivity. The IUCN notes that it is difficult to feed, so many collected fish starve, and Animal Diversity Web gives an average captive lifespan of 2 to 4 years against 10 to 15 years in the wild. FishBase records that it has been reared in captivity, but the IUCN says most traded fish are still caught wild.
Did you know?
A mandarinfish has no scales at all.
Instead of scales, a mandarinfish is covered in thick slime that smells bad and tastes bitter to other animals.
The scaleless skin is covered in a bitter, foul-smelling mucus, and sacciform skin cells release substances with some toxins (Animal Diversity Web).
No scales, slimy skin
A mandarinfish has no scales.
Its skin is covered in slime. The slime smells bad, so other fish leave it alone. It has big fan fins under its head.
The mandarinfish has no scales. Instead, its skin is coated in thick mucus, or slime. The Oregon Coast Aquarium says this coat helps protect it from parasites and predators, and Animal Diversity Web says the mucus smells unpleasant and tastes bitter.
Under its head are large, fan-like pelvic fins. The mandarinfish uses them to walk and hop along the reef floor.
The skin is scaleless and covered by a thick mucus layer. Animal Diversity Web reports that the mucus has an unpleasant smell and bitter taste, and that a layer of sacciform cells releases substances with some toxins; the secretion is suggested to repel predators and competitors. The Oregon Coast Aquarium describes the mucus as protection against parasites and predators.
Why the fish is so brightly colored is not known. Animal Diversity Web suggests the colors may act as a warning (aposematism), though this is a hypothesis. The large, fan-like pelvic fins are used to walk along the bottom, and males have a much longer first dorsal spine than females.
A sunset dance
At sunset, a mother and father fish swim up together.
They let go of tiny eggs. The eggs float away. Baby fish hatch and later settle on the reef.
Mandarinfish spawn at dusk. A male courts a female with a stop-start dance, his fins spread wide. Then the pair rise together toward the surface and release eggs and sperm into the water.
A female lays between 12 and 205 tiny eggs at a time. The eggs float and drift with the currents. Within about 8 to 9 days of hatching, the young fish settle on a reef, where they stay in a small area for at least a month.
Spawning occurs at dusk: the male courts with extended fins and stop-start movements (Oregon Coast Aquarium), then the pair align and rise about a meter above the reef to release gametes, so fertilization is external (Animal Diversity Web). Females spawn once a night or every few days and release 12 to 205 buoyant, pelagic eggs; larger males mate more often.
There is no parental care. Juveniles settle on the reef within 8 to 9 days of hatching and stay in a small area for at least a month (IUCN). The adult color pattern appears in the second month, at 10 to 15 millimeters (Animal Diversity Web), and maturity comes at about 3 centimeters total length, or 14 months (IUCN).
Slow, shy and careful
Mandarinfish are slow and shy.
In the daytime they hide in cracks and coral. They often live in pairs or small groups.
Mandarinfish are slow, shy fish. During the day they move carefully along coral branches or hide in their favorite cracks in the reef.
They are usually seen in pairs or small groups. As night falls, small groups of males and females gather on parts of the reef to spawn, and the males compete to be chosen by the females.
Animal Diversity Web describes the species as slow, shy and mostly passive, usually seen in pairs or groups; in daylight individuals move along coral branches or shelter in home crevices. Small spawning groups of males and females gather on particular parts of the reef at night.
Because there are few active females, males compete, and larger males spawn more often. In aquariums males are aggressive to one another, and two males usually cannot be kept together. The IUCN notes that the species has few natural predators.
Did you know?
Mandarinfish use their fins to hop along the bottom.
Mandarinfish use their big, fan-like pelvic fins to walk along the reef floor.
The large pelvic fins are used often to walk over the bottom rather than for open-water swimming (Animal Diversity Web).
Too popular in aquariums?
Many mandarinfish still live in the sea.
But people catch lots of them for fish tanks. Scientists are keeping an eye on them.
The IUCN lists the mandarinfish as Least Concern, because it lives across a wide area and is not heavily fished in most places.
But it is one of the 20 sea fish brought into the United States most often for aquariums, and most are caught from the wild. In parts of the Philippines, where many have been collected since the 1980s, there are now fewer of them. Scientists say the trade should be watched closely.
The IUCN assessed the mandarinfish as Least Concern (assessed October 2018, published 2019), with an unknown population trend. It has been heavily collected for the international aquarium trade in the Philippines since the 1980s and more recently in Indonesia, and it is among the top 20 marine aquarium fish imported to the United States.
Fishers off Batasan Island in the Philippines reported falling numbers and smaller fish, and declines have been documented elsewhere in the Philippines. Because large males are targeted, there is concern about unbalanced sex ratios. The IUCN calls rising aquarium demand a cause for concern; there are no species-specific conservation measures.
IUCN Red List
How is the mandarinfish doing in the wild?
- Least Concern (this animal)
- Near Threatened
- Vulnerable
- Endangered
- Critically Endangered
- Extinct in the Wild
- Extinct
Least Concern
Not at risk of disappearing from the wild right now.
See the IUCN Red List assessment · The IUCN Red List of Threatened Species 2022.2
Amazing facts
-
A mandarinfish has no scales at all.
Instead of scales, a mandarinfish is covered in thick slime that smells bad and tastes bitter to other animals.
The scaleless skin is covered in a bitter, foul-smelling mucus, and sacciform skin cells release substances with some toxins (Animal Diversity Web).
-
Mandarinfish use their fins to hop along the bottom.
Mandarinfish use their big, fan-like pelvic fins to walk along the reef floor.
The large pelvic fins are used often to walk over the bottom rather than for open-water swimming (Animal Diversity Web).
-
Mandarinfish dance at sunset.
A male mandarinfish courts a female with a stop-start dance, fins spread wide, before the pair rise together to spawn.
Courtship involves extended fins and stop-start movements (Oregon Coast Aquarium), followed by a paired rise of about a meter above the reef to release gametes.
-
Wild mandarinfish can live for many years.
In the wild, a mandarinfish can live 10 to 15 years, but in aquariums most live only a few years.
Wild longevity is given as 10 to 15 years (IUCN), against an average of 2 to 4 years in captivity (Animal Diversity Web), largely because of its specialized diet.
Words to know
- dragonet
- a member of a family of small, bottom-living fish that includes the mandarinfish
- mucus
- a thick, slippery slime
- scales
- small, hard plates that cover the skin of many fish
- spawn
- to release eggs and sperm into the water
- crustacean
- an animal with a hard outer shell and jointed legs, such as a shrimp or crab
- dusk
- the time of evening when the sun has just gone down
Discovery challenge
-
What covers a mandarinfish's skin?
What covers a mandarinfish's skin instead of scales?
What protects the mandarinfish's scaleless skin?
- Feathers
- Thick slime
- Hard shell plates
Show the answer
Thick slime
Its skin is covered in slime, not scales.
It has no scales. Thick, bad-smelling slime covers its skin instead.
A thick, bitter, foul-smelling mucus layer, with skin cells that release some toxins.
-
When do mandarinfish dance and lay eggs?
At what time of day do mandarinfish spawn?
When does Synchiropus splendidus usually spawn?
- Early morning
- Noon
- Dusk
Show the answer
Dusk
They dance at sunset, when the day is ending.
At dusk, a pair rises toward the surface together to release eggs.
Spawning happens at dusk, when pairs rise from the reef and release buoyant eggs.
-
What does a mandarinfish eat?
What does a mandarinfish mostly eat?
Which best describes the mandarinfish's diet?
- Tiny animals on the reef floor
- Big fish
- Seaweed only
Show the answer
Tiny animals on the reef floor
It eats very tiny animals that it finds on rocks and sand.
It picks small crustaceans, worms and other tiny creatures off the reef floor.
Small benthic crustaceans such as amphipods and isopods, small worms and protozoans.
-
Where do mandarinfish live?
In which ocean do mandarinfish live?
Which region holds the mandarinfish's native range?
- The western Pacific Ocean
- The Arctic Ocean
- Rivers in Europe
Show the answer
The western Pacific Ocean
They live on coral reefs in the warm western Pacific Ocean.
They live on shallow reefs from southern Japan to Australia and New Caledonia.
The tropical western Pacific, from the Ryukyu Islands to Queensland, Vanuatu and New Caledonia.
Places where you might see it
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Watch
Country
Philippines
The Philippines is an island country in Southeast Asia, in the western Pacific Ocean. It has more than 7,000 islands, about 50 volcanoes and rich coral reefs, and about 112.7 million people were counted there in 2024.
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Watch
Country
Indonesia
Indonesia is a country of about 17,500 islands in Southeast Asia, spread across the Equator between the Indian and Pacific oceans. It has more than 100 active volcanoes, rainforests full of wildlife, and about 286 million people (2025).
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Watch
Country
Australia
Australia is a country and the smallest continent, surrounded by ocean in the Southern Hemisphere. Much of its middle is dry and flat, most people live near the coast, and its animals include kangaroos, koalas and the platypus, a mammal that lays eggs.
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For parents & teachers
What children will learn
- Describe how the mandarinfish's skin differs from most fish (no scales, protective mucus).
- Explain the mandarinfish's life cycle, from dusk spawning to floating eggs and settlement on the reef.
- Understand how collection for the aquarium trade can affect a wild fish population.
Recommended ages: 3 to 17 · About 10 minutes
Talk about it
- Why might a slimy, bad-tasting skin help a small, slow fish survive?
- Scientists are not sure why the mandarinfish is so colorful. What ideas could you test?
- What questions should someone ask before buying a wild-caught fish for an aquarium?
Try at home or in class
- Measure 9 centimeters on a ruler and compare it with your hand: that is the biggest a mandarinfish grows.
- Draw a mandarinfish with wavy orange, blue and green lines, then design your own reef fish pattern.
Key vocabulary: dragonet, mucus, scales, spawn, crustacean, dusk
Where these facts come from
- The IUCN Red List of Threatened Species , International Union for Conservation of Nature (IUCN terms of use (no redistribution of Red List data or range maps))
- GBIF Backbone Taxonomy and GBIF Occurrence Search , Global Biodiversity Information Facility (CC0 1.0 (backbone); occurrence counts are facts derived from records under CC0, CC BY and CC BY-NC)
- Synchiropus splendidus (Mandarinfish), 2019 global assessment , IUCN Red List of Threatened Species
- Synchiropus splendidus, Mandarinfish: species summary , FishBase
- Synchiropus splendidus (Mandarin-fish) , Animal Diversity Web, University of Michigan Museum of Zoology
- Mandarin goby , Oregon Coast Aquarium
- Wikidata , Wikimedia Foundation (CC0 1.0)
- Wikimedia Commons , Wikimedia Foundation (Per file: Public domain, CC0, CC BY or CC BY-SA only (credited on each page))
Checked, not yet human-reviewed. Last updated October 27, 2026. Spotted a mistake? Tell us.