Animal
Yellow boxfish
The yellow boxfish is shaped like a box. Young ones are bright yellow with black spots. Its body is covered in hard plates, like a suit of armor.
The yellow boxfish lives inside its own box: a hard shell of bony plates joined together, with holes for its eyes, mouth and fins. Young boxfish are bright yellow with black polka dots, and big adults turn bluish. Its skin can release a toxic slime that protects it from predators, and it paddles slowly around reefs nibbling algae and small animals.
Ostracion cubicus (now spelled Ostracion cubicum by the IUCN) is a boxfish (family Ostraciidae, order Tetraodontiformes) of Indo-Pacific reefs. Its body is enclosed in a rigid carapace of fused bony plates, its skin secretes a toxic mucus, and its color changes from spotted yellow juvenile to bluish adult. The IUCN lists it as Least Concern (assessed 2023, published 2024).
Photo: J. Petersen, CC BY 2.5, via Wikimedia Commons
Meet the yellow boxfish
The yellow boxfish looks like a little box with fins.
Young ones are bright yellow with black dots. Its body is hard, like a shell. It swims slowly and wiggles its fins.
The yellow boxfish really is shaped like a box. Its body is wrapped in a hard shell made of bony plates fitted together, with openings for its mouth, eyes, fins and tail.
Young yellow boxfish are bright yellow with black spots about the size of the pupil of their eye. As they grow, the spots get smaller, the yellow turns a dull mustard color, and the biggest adults become bluish with yellow lines along the edges of their plates.
Ostracion cubicus is a ray-finned fish (class Actinopterygii) in the boxfish family, Ostraciidae, part of the order Tetraodontiformes with pufferfishes and porcupinefishes. The IUCN now uses the spelling Ostracion cubicum and calls cubicus an orthographic error; the Red Sea population, slightly different in color, was once named Ostracion argus.
Its body is enclosed in a carapace of bony plates with openings for the mouth, eyes and fins (Nausicaa). FishBase describes the color change: juveniles bright yellow with black spots, which shrink as the yellow dulls to mustard, and large adults bluish with yellowish seams between the plates. Maximum total length is 45 centimeters (IUCN).
Quick facts
- Group
- Fish
- Length
- up to 45 cm
Sheltered reefs and lagoons
Yellow boxfish live in warm seas.
They live on coral reefs and in quiet lagoons. Little ones hide in tiny cracks and among branching corals.
Yellow boxfish live across the Indian and Pacific Oceans, from the Red Sea, the Persian Gulf and East Africa to the Tuamotu Islands in French Polynesia, and from southern Japan to Australia and northern New Zealand. They also live around Hawaii and along South Africa's south coast.
They live in sheltered coastal and offshore coral reefs, sandy lagoons, seaweed meadows, cracks and overhangs, from about 1 to 75 meters deep. Adults often stay near ledges and crevices where they can shelter.
The IUCN range runs from the Red Sea, Persian Gulf and East and South Africa (to Knysna) across the Indian Ocean islands to the Tuamotu Archipelago, north to southern Japan and the Ryukyu and Ogasawara Islands, south to New Caledonia, Australia (Fremantle around the north to Wollongong), Lord Howe and Norfolk Islands and northern New Zealand, and to Rapa and the Hawaiian Islands, at 1 to 75 meters.
It inhabits sheltered coastal and offshore coral reefs and flat bottoms (IUCN); Nausicaa adds sandy lagoon areas, seaweed meadows and overhangs. The Australian Museum notes coral and rocky reefs to 40 meters, with adults on deeper coastal slopes and lagoons with crevices and ledges. The IUCN recorded about 60 fish per hectare at Moorea in French Polynesia (1990 to 1993).
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
Reefs and lagoons from the Red Sea, Persian Gulf and East and South Africa to the Tuamotu Islands, Hawaii, southern Japan, Australia and northern New Zealand. In the United States it lives only around Hawaii. The IUCN also lists many islands too small to shade here, including the Maldives, Seychelles, Mauritius, Palau, Guam and French Polynesia.
Places: Australia, Brunei, Cambodia, China, Djibouti, Egypt, Eritrea, Fiji and 33 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 Australia, Indonesia, Egypt, New Caledonia, Japan, Philippines, Thailand, South Africa and 47 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.
Nibbling algae and small animals
Yellow boxfish eat mostly algae, a kind of sea plant.
They also eat tiny animals, worms, crabs and snails that they find on the reef.
Yellow boxfish eat mainly algae, the simple plant-like living things that grow on rocks. They also nibble many small animals: sponges, tiny crabs and shrimps, snails and clams, worms that live in the sand, and the occasional small fish.
They find their food on the reef floor and in sandy patches, moving slowly and carefully.
The IUCN gives a diet primarily of algae, with microorganisms, small fishes and benthic invertebrates such as sponges, crustaceans, molluscs, polychaete worms, foraminiferans and live corals. FishBase lists sand-dwelling polychaetes among them, and the Australian Museum describes it feeding on a range of benthic organisms.
Did you know?
A boxfish helped people design a car!
The boxfish's shape inspired the design of a car called the Mercedes-Benz Bionic.
Nausicaa notes that the boxfish's shape and hydrodynamics inspired the Mercedes-Benz Bionic car, an example of biomimicry.
A fish in a box
A boxfish's body is covered in hard plates.
The plates fit together like tiles. Its skin can make a slime that keeps other fish away.
A boxfish's body is enclosed in a hard carapace, a shell of bony plates joined together like floor tiles. Only its fins, tail, eyes and mouth stick out. It swims by moving its fins, and it can hover, swim backward and turn around.
Its skin also makes a highly toxic slime, called mucus, which protects it from predators. Few animals eat boxfish; one that does is the giant humphead wrasse.
The carapace is formed of bony plates with openings for the mouth, eyes and fins (Nausicaa); the seams between plates show as yellowish lines in large adults (FishBase). The dorsal fin has 8 to 9 soft rays and no spines, and the anal fin 9 soft rays.
Nausicaa states that the skin secretes a highly toxic mucus that protects the fish from predators. Despite these defenses, the humphead wrasse is one of the few predators known to eat boxfishes (FishBase). The yellow boxfish in this photo was seen in the wild off Bunaken Island, North Sulawesi, Indonesia, and is a large adult in its bluish coloring.
From polka dots to blue
Boxfish eggs float away in the sea.
Babies are tiny and bright yellow with black dots. As they grow up, the dots get smaller.
Yellow boxfish lay eggs that float away in the current. The tiny young drift in the open sea, then settle on sheltered reefs. In New South Wales, Australia, this happens in summer, when small groups of young boxfish can be found together.
The little ones are bright yellow with black dots and hide in narrow cracks or among branching corals. As they grow, their dots get smaller and their color fades to mustard, and the biggest adults turn bluish.
The species lays eggs that are released into the current (Nausicaa). The IUCN describes it as gonochoristic (separate sexes, rather than changing sex), living in harems of a single male and 2 to 4 females. Larvae are pelagic; some juveniles are carried into the subtropical zone before settling.
The Australian Museum notes that larvae settle on sheltered rocky and coral reefs, in summer in New South Wales, where juveniles often form small aggregations. Small juveniles are secretive in narrow crevices or among Acropora corals. With growth, the pupil-sized black spots shrink and may turn brownish or white with a black margin.
A slow swimmer with clever fins
The boxfish swims slowly.
It can swim forward, backward and spin around. Grown-ups usually live alone.
A yellow boxfish is not a fast swimmer, but it is very nimble. Using its fins, it can hover on the spot, swim backward and turn around in a tight space. Nausicaa, a big aquarium in France, calls its way of swimming the 'gondolier style'.
Adults usually live alone. At breeding time, one male may live with two to four females.
Nausicaa describes a slow but highly maneuverable swimmer that can hold position, move backward and turn using its fins, a style it calls 'gondolier'. Its box shape and hydrodynamics inspired the design of a car, the Mercedes-Benz Bionic.
Adults are mostly solitary (IUCN; FishBase), but form harems of one male and 2 to 4 females (IUCN; Nausicaa says at breeding time). Nausicaa also describes them in aquariums as shy and curious, watching what happens on the other side of the glass.
Did you know?
Baby boxfish are bright yellow with black dots.
Young yellow boxfish have black spots about the size of the pupil of their eye.
Juvenile spots are pupil-sized; they shrink with growth and can turn white with a black margin (Australian Museum).
Common on many reefs
Yellow boxfish are not in danger.
They live in lots of warm seas. Some people catch them to keep in fish tanks.
The IUCN lists the yellow boxfish as Least Concern. It lives across a huge area and is common in places such as French Polynesia and the Philippines.
Some are caught for home aquariums, for decorations or for food, but scientists do not yet know whether this harms the population.
The IUCN assessed the species as Least Concern (assessed 18 August 2023, published 2024), with an unknown population trend and no known major threats. It is common and abundant in French Polynesia and the Philippines and is known from at least 1,073 museum specimens.
It is harvested for the aquarium trade, for ornaments and for food, with unknown impact. In 2011, 5,971 were imported into the United States for aquariums, ranking it 143rd among imported aquarium fish. In Myanmar it is caught in bottom trawls and gill nets. There are no species-specific conservation measures.
IUCN Red List
How is the yellow boxfish 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.
Amazing facts
-
A boxfish helped people design a car!
The boxfish's shape inspired the design of a car called the Mercedes-Benz Bionic.
Nausicaa notes that the boxfish's shape and hydrodynamics inspired the Mercedes-Benz Bionic car, an example of biomimicry.
-
A boxfish can swim backward.
A boxfish swims with its fins, so it can hover, swim backward and spin around.
Fin-powered locomotion lets it hold position, reverse and turn; Nausicaa calls it the 'gondolier style'.
-
Baby boxfish are bright yellow with black dots.
Young yellow boxfish have black spots about the size of the pupil of their eye.
Juvenile spots are pupil-sized; they shrink with growth and can turn white with a black margin (Australian Museum).
-
Big humphead wrasses can eat boxfish.
Few animals eat boxfish, but the giant humphead wrasse is one that does.
FishBase lists boxfishes among the toxic prey of the humphead wrasse.
Words to know
- carapace
- a hard shell that covers an animal's body
- mucus
- a thick, slippery slime
- toxic
- poisonous; harmful if touched or eaten
- algae
- simple plant-like living things that grow in water
- harem
- a group of females that live with one male
- biomimicry
- copying ideas from nature to design new things
Discovery challenge
-
What covers a boxfish's body?
What makes up the yellow boxfish's 'box'?
What is the boxfish's carapace made of?
- Bony plates
- Feathers
- Soft fur
Show the answer
Bony plates
Hard plates fit together to make its box.
Bony plates join together into a stiff shell, with openings for the eyes, mouth and fins.
A rigid carapace of bony plates, with seams visible in large adults.
-
What color is a baby yellow boxfish?
What does a young yellow boxfish look like?
Which describes the juvenile coloration of Ostracion cubicus?
- Bright yellow with black spots
- Plain gray
- Red with white stripes
Show the answer
Bright yellow with black spots
Babies are bright yellow with black dots.
Young ones are bright yellow with black spots; older ones fade to mustard and then bluish.
Bright yellow with pupil-sized black spots, which shrink as the fish grows.
-
How does a boxfish keep safe?
Besides its armor, how does a yellow boxfish protect itself?
Which defense does the yellow boxfish's skin provide?
- It swims very fast
- Its skin makes a toxic slime
- It changes into a rock
Show the answer
Its skin makes a toxic slime
Its skin can make a slime that other fish don't like.
Its skin releases a highly toxic slime, called mucus, that protects it from predators.
The skin secretes a highly toxic mucus that deters predators.
-
What does a yellow boxfish mostly eat?
What is the main food of the yellow boxfish?
What does Ostracion cubicus feed on primarily?
- Algae
- Big fish
- Seeds from trees
Show the answer
Algae
It eats mostly algae, plus tiny animals.
It eats mainly algae, plus sponges, small crustaceans, snails, worms and small fish.
Primarily algae, with microorganisms, small fishes and benthic invertebrates.
Places where you might see it
-
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).
-
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.
-
Watch
Country
Japan
Japan is an island country in East Asia. Most of its land is steep mountains and forest, Mount Fuji is its tallest peak, and about 124 million people live there, many of them in big cities such as Tokyo.
Explore next
-
Watch
Animal
Spot-fin porcupinefish
The spot-fin porcupinefish is a spiny relative of the pufferfish that lives on warm reefs all around the world. Its spines usually lie flat, but when it is threatened it swallows water and swells into a prickly ball. At night it uses a strong, beak-like mouth to crack open snails, hermit crabs and sea urchins.
-
Watch
Animal
Humphead wrasse
The humphead wrasse is the biggest fish in the wrasse family, up to about 2.3 meters long. Adults have thick lips, a forehead hump and wavy lines on the face. They eat shellfish, sea urchins and even toxic crown-of-thorns starfish, and many change from female to male. Too many have been caught, so it is endangered.
-
Watch
Animal
Emperor angelfish
The emperor angelfish is a striped reef fish from the Indian and Pacific Oceans. Adults are blue with bright yellow stripes, a yellow tail and a dark mask across the eyes. Young ones are dark blue with white and blue rings, and they change color as they grow. Emperor angelfish nibble sponges on the reef.
-
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).
-
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.
-
Watch
Country
Japan
Japan is an island country in East Asia. Most of its land is steep mountains and forest, Mount Fuji is its tallest peak, and about 124 million people live there, many of them in big cities such as Tokyo.
-
Watch
Animal
Alligator gar
The alligator gar is one of the largest freshwater fish in North America. It has a broad snout lined with teeth, armor-like scales, and a swim bladder that works like a lung, so it can gulp air in warm, still water. It lives in the big rivers, swamps and bayous of the southern United States, Mexico and Central America.
-
Watch
Animal
Arapaima
The arapaima is one of the biggest freshwater fish in the world, longer than a grown-up is tall. It lives in the warm, slow rivers and flooded lakes of the Amazon, and it must swim up to the surface to gulp air every few minutes.
For parents & teachers
What children will learn
- Describe how the yellow boxfish's carapace and toxic mucus protect it.
- Explain how a fish inside a hard shell swims using its fins.
- Describe the yellow boxfish's color change from juvenile to adult.
Recommended ages: 3 to 17 · About 10 minutes
Talk about it
- What are the good and bad points of having a hard shell instead of being fast?
- Why might engineers look at animals like the boxfish when designing cars or boats?
- Why might a young fish look so different from an adult of the same kind?
Try at home or in class
- Make a 'boxfish' from a small cardboard box with paper fins, then try moving it through a tub of water using only the fins.
- Draw a young yellow boxfish with black polka dots and an adult with bluish plates side by side.
Key vocabulary: carapace, mucus, toxic, algae, harem, biomimicry
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)
- Ostracion cubicum (Yellow Boxfish), 2024 global assessment , IUCN Red List of Threatened Species
- Yellow Boxfish, Ostracion cubicus , Australian Museum
- Yellow boxfish , Nausicaa, Centre National de la Mer
- Ostracion cubicum, Yellow boxfish: species summary , FishBase
- 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 28, 2026. Spotted a mistake? Tell us.