Animal
Siamese fighting fish
The Siamese fighting fish, or betta, is a small fish from Thailand. Pet bettas have long, flowing fins in bright colors. They can breathe air from the top of the water!
The Siamese fighting fish, often called the betta, is a small freshwater fish from shallow, warm waters in Thailand. It can breathe air with a special organ, and males build nests of bubbles for their eggs. People have bred bettas for many centuries, giving pet bettas their bright colors and long fins.
Betta splendens is a labyrinth fish native to Thailand's shallow, low-oxygen wetlands, where wild fish are dull brown or green. Domesticated for at least 1,000 years according to a genomic study, and bred for color and fins since the early twentieth century, it is now one of the world's most popular aquarium fish. Wild populations are listed as Vulnerable by the IUCN.
Photo: Henryk Niestrój, CC BY 4.0, via Wikimedia Commons
Meet the betta
The Siamese fighting fish is a small fish. Many people call it a betta.
Pet bettas have long, flowing fins in red, blue and many other colors. Wild bettas are plain brown or green.
The Siamese fighting fish, usually called the betta, is a small freshwater fish that grows to about 6.5 centimeters long. Wild bettas come from Thailand, in Southeast Asia.
Pet bettas are famous for their bright colors and long, flowing fins. Those were created by people choosing which fish to breed, over and over, for many generations. Wild bettas look very different: they are dull brown or green, with much shorter fins.
Betta splendens belongs to the family Osphronemidae within the labyrinth fishes (suborder Anabantoidei). The University of Florida's extension service notes that the genus Betta, with over 73 species, is the most diverse group in its family. B. splendens is part of the B. splendens species complex of closely related species from the Malay Peninsula region.
Wild fish are dull brown or green. The vivid colors and elaborate fins of pet bettas come from selective breeding; a 2021 genomic study found that the genes selected by breeders have large effects on color in particular body regions and on the shape of individual fins, and that most of them are inherited independently, which helps explain the enormous variety of ornamental bettas.
Quick facts
- Group
- Fish
- Length
- up to 0.07 m
- Lifespan in the wild
- up to 2 years
Where it lives
Wild bettas live in Thailand.
They live in shallow, warm water, like ponds, rice fields and even puddles. The water is full of plants.
Wild Siamese fighting fish live in Thailand, in shallow, still water: ponds, rice paddies and even puddles. The water is warm, often thick with plants, and sometimes has very little oxygen in it.
Scientists who studied one wild population in Thailand found the fish in water only about 5 centimeters deep on average, at around 30 degrees Celsius. Today, of course, pet bettas live in homes all over the world, but the IUCN lists wild populations only in Thailand.
The IUCN lists the species as native to Thailand. In the wild it lives in standing water such as shallow ponds, rice paddies and puddles. A study of one Thai population summarized by the University of Florida found heavy emergent vegetation, an average depth of about 5 centimeters, temperatures around 29.9 degrees Celsius, acidic water of about pH 5.5, and dissolved oxygen averaging 3.8 milligrams per liter but swinging from 0 to about 7.4 over the day.
The fish lived at low density, about 1.7 per square meter, with 1.4 females for each male. In April and May, the breeding season in Thailand, bettas move to shallow water edges to breed. Ornamental bettas are kept worldwide, but they are domestic animals, not wild populations.
Continent
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
Wild populations in shallow ponds, rice paddies and marshes of Thailand, as listed by the IUCN. Pet bettas are kept worldwide but are domesticated, not wild; occasional wild records elsewhere in Southeast Asia are not shown.
Places: Thailand.
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 Thailand, Cuba, Vietnam, Indonesia, Colombia, Australia, Malaysia, Brazil and 11 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.
Snacks from the surface
Bettas eat tiny animals, like insects.
Their mouths point up, so they can grab food from the top of the water.
A betta's mouth points upward. That shape helps it snap up food at the surface of the water.
In the wild, bettas mostly eat insects that fall into the water. Baby bettas start on very tiny living things. On betta farms, babies are fed tiny water creatures and baby brine shrimp, then switched to flakes or pellets as they grow.
The upturned mouth suits surface feeding. The Animal Diversity Web account describes wild bettas eating mainly insects that fall into the water, and lists five observed feeding methods: snapping, scooping or gulping, grazing, jumping and spitting, with snapping the most common.
In aquaculture, the University of Florida explains, larvae are first fed live foods of an appropriate size, such as infusoria (mixtures of very small aquatic organisms) and brine shrimp nauplii, and are later weaned onto commercial flake or pelleted diets.
Did you know?
Bettas can breathe air from the top of the water.
Bettas have a labyrinth organ above their gills that lets them breathe air gulped at the surface.
The labyrinth organ, folded bony plates lined with respiratory tissue in chambers above the gills, lets bettas breathe air; many labyrinth fishes are obligate air breathers.
A fish that breathes air
Bettas have a special part in their head that lets them breathe air.
They swim up and gulp air from the top of the water. That helps them live in water with little oxygen.
Bettas belong to a group called labyrinth fishes. Above their gills they have a pair of chambers holding a folded, maze-like organ called the labyrinth organ. It lets them take in oxygen from air they gulp at the surface.
This is very useful in warm, shallow water that can run out of oxygen. In fact, many labyrinth fishes must come up for air to survive. Bettas also have scales that overlap like roof shingles, and long fins that help them balance and turn.
Labyrinth fishes have relatively small gills, which mainly excrete ammonia and carbon dioxide; many species are obligate air breathers. Paired chambers above the gills, extensions of the first gill arch, contain folded bony plates covered with respiratory tissue: the labyrinth organ. The University of Florida links the group's evolution, about 60 million years ago, to warm, low-oxygen habitats.
Air breathing is tied to other traits that evolved with it, such as bubble-nest building. The body is covered by overlapping scales coated in mucus, and the Animal Diversity Web notes that color comes from pigment cells called chromatophores; the fins provide propulsion, balance and turning.
A father's bubble nest
Betta dads build nests made of bubbles at the top of the water.
They put the eggs in the bubbles and guard them. The babies hatch in a day or two.
Male bettas build floating nests out of bubbles. A male gulps air at the surface and blows out sticky, mucus-coated bubbles, one after another, until he has a little raft.
When a female is ready, she releases a few eggs at a time, and the male catches them in his mouth and places them in the nest, around 300 eggs in all. Then the male takes over. He guards the nest, adds bubbles when needed and keeps the newly hatched babies in the nest. The eggs hatch in about one to two days.
Bubble nest building is part of the labyrinth fishes' adaptation to warm, low-oxygen water. The University of Florida explains that the nest keeps eggs at the surface, where oxygen exchange is greater, protects them from drying out and keeps them relatively free of predators.
During spawning the male wraps around the female and fertilizes the eggs as she releases them a few at a time; he collects the sinking eggs in his mouth and places them in the nest, with about 300 eggs per spawning. The male then tends the eggs and larvae. Eggs hatch in about 24 to 48 hours, depending on temperature (Animal Diversity Web), and larvae absorb their yolk sacs about 3 days after hatching. Males and females become distinguishable at 3 to 4 months.
Why male bettas live alone
Boy bettas do not get along with other boy bettas.
When two meet, they spread their fins and puff out their gill covers. So pet boy bettas each live in their own tank.
Male bettas defend their space and their nests. When a male meets another male, he quickly puts on a display: he spreads his fins wide and flares out his gill covers. If neither backs down, they bite each other's fins and sides and can get hurt.
That is why people keep male bettas apart. On betta farms, young fish grow up together until they are 3 to 4 months old. Then the males are moved into their own containers so they cannot hurt each other.
Aggression is common in labyrinth fishes, especially among males defending nests, and the University of Florida describes betta males as among the most aggressive. A male meeting another male almost immediately spreads his fins and flares his gill covers; if the encounter continues, the fish bite each other, particularly on the fins and flanks.
For this reason males are separated. In commercial culture, young bettas are reared together until 3 to 4 months, when males become distinguishable and must be moved into individual containers to avoid injury, while females are reared together. Historically, males were selected in Thailand for aggression because contests between males were used for gambling; today breeding focuses on appearance, although male aggression remains.
Did you know?
The betta is Thailand's national water animal.
Thailand's National Identity Committee has named the betta the country's national aquatic animal.
In recognition of its cultural significance, Thailand's National Identity Committee designated the betta the national aquatic animal.
Bettas and people
People in Thailand have kept bettas for a very, very long time.
Now bettas are one of the most popular pet fish in the world. The betta is Thailand's national water animal.
People in Southeast Asia have been breeding Siamese fighting fish for a very long time. A study of betta DNA suggests they were first domesticated at least 1,000 years ago. About 100 years ago, people began breeding them for beauty, and they became one of the world's most popular pet fish.
Thailand has named the betta its national aquatic animal. Huge numbers are raised on farms there: more than 100,000 male bettas are shipped from Thailand every week to pet stores around the world.
A genomic study (Kwon and colleagues, posted 2021) estimated from pedigree-based mutation rates that bettas were domesticated at least 1,000 years ago, centuries earlier than previously thought, and found that ornamental bettas carry genetic contributions from two related wild species, B. imbellis and B. mahachaiensis, while domestic genes have also entered wild populations. It also identified dmrt1 as the main sex-determination gene in ornamental bettas.
The authors note reports of fighting-fish breeding in Thailand as early as the 14th century, and ornamental breeding from the early 20th century. The University of Florida reports that over 100,000 male bettas are shipped weekly, mainly from Thailand, and that Thailand's National Identity Committee has designated the betta the national aquatic animal.
Did you know?
Betta dads build nests out of bubbles.
Male bettas blow sticky, mucus-coated bubbles to build floating nests for their eggs.
The male's bubble nest keeps eggs at the oxygen-rich surface, prevents drying and keeps them relatively safe from predators.
Wild bettas need help
There are lots of pet bettas, but wild bettas are in trouble.
The ponds and wetlands where they live are being changed or polluted.
It may be surprising, but while pet bettas are everywhere, wild Siamese fighting fish are listed as Vulnerable. Their numbers in the wild are going down.
The shallow wetlands where they live are being changed by dams and water use, disturbed by people working there, and polluted by waste water from towns, factories and farms. Another problem is that genes from pet bettas are mixing into wild populations.
The IUCN assessed Betta splendens in February 2011 as Vulnerable under criteria A2ace, with a decreasing population; the assessment is flagged as needing an update. Listed threats include human disturbance from work and other activities, dams and water management, introduced genetic material, and domestic, urban and industrial wastewater.
The introduced-genetics concern is supported by the 2021 genomic study, which found ornamental betta ancestry in wild B. splendens and B. mahachaiensis populations.
Did you know?
Wild bettas are brown or green, not bright like pet bettas.
Wild bettas are dull brown or green. The bright colors of pet bettas were created by breeders.
Wild B. splendens are dull brown or green; genomic work shows breeders selected genes with large effects on color in specific body regions.
Amazing facts
-
Bettas can breathe air from the top of the water.
Bettas have a labyrinth organ above their gills that lets them breathe air gulped at the surface.
The labyrinth organ, folded bony plates lined with respiratory tissue in chambers above the gills, lets bettas breathe air; many labyrinth fishes are obligate air breathers.
-
Betta dads build nests out of bubbles.
Male bettas blow sticky, mucus-coated bubbles to build floating nests for their eggs.
The male's bubble nest keeps eggs at the oxygen-rich surface, prevents drying and keeps them relatively safe from predators.
-
The betta is Thailand's national water animal.
Thailand's National Identity Committee has named the betta the country's national aquatic animal.
In recognition of its cultural significance, Thailand's National Identity Committee designated the betta the national aquatic animal.
-
Wild bettas are brown or green, not bright like pet bettas.
Wild bettas are dull brown or green. The bright colors of pet bettas were created by breeders.
Wild B. splendens are dull brown or green; genomic work shows breeders selected genes with large effects on color in specific body regions.
Words to know
- labyrinth organ
- a maze-like organ above a fish's gills that lets it breathe air
- bubble nest
- a floating raft of bubbles that some fish build to hold their eggs
- display
- a way an animal shows itself off, for example by spreading its fins
- domesticated
- bred by people over many generations to live with them
- selective breeding
- choosing which animals have young, to bring out certain features
- rice paddy
- a flooded field where rice grows
Discovery challenge
-
How can a betta breathe air?
Which special organ lets a betta breathe air?
Which structure allows Betta splendens to breathe atmospheric air?
- Its labyrinth organ
- Its tail
- Its scales
Show the answer
Its labyrinth organ
A special part called the labyrinth organ lets it breathe air.
The labyrinth organ, above the gills, takes in oxygen from air the betta gulps at the surface.
Paired chambers above the gills hold the labyrinth organ, folded bony plates lined with respiratory epithelium.
-
Who looks after betta eggs?
Which parent looks after betta eggs?
Which parent tends the bubble nest?
- The father
- The mother
- Nobody
Show the answer
The father
The dad builds a bubble nest and looks after the eggs.
The male builds the bubble nest, places the eggs in it and guards them.
The male builds and maintains the nest and tends the eggs and larvae; the female is not involved after spawning.
-
Why do pet boy bettas live in their own tanks?
Why are male bettas kept apart from each other?
Why must male bettas be separated in culture?
- They do not get along and can hurt each other
- They are too shy to swim
- They need to sleep in the dark
Show the answer
They do not get along and can hurt each other
Boy bettas don't get along. Living apart keeps them safe.
Males display, then bite each other's fins and sides, so they are kept apart to avoid injury.
Males become aggressive toward other males; on farms they are moved into individual containers at 3 to 4 months to prevent damage.
-
Where do wild bettas live?
In which country do wild Siamese fighting fish live?
Which country does the IUCN list as the native range of Betta splendens?
- Thailand
- Iceland
- Brazil
Show the answer
Thailand
Wild bettas live in Thailand, in warm, shallow water.
They live in shallow ponds, rice paddies and puddles in Thailand.
The IUCN lists Thailand; wild fish occupy shallow, vegetated, low-oxygen waters.
Places where you might see it
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For parents & teachers
What children will learn
- Explain how the labyrinth organ lets bettas breathe air and why that helps in warm, shallow water.
- Describe the bubble nest and the male's role in caring for eggs and young.
- Explain why male bettas are kept apart, using their displays as the example.
- Understand the difference between wild bettas and the domesticated pet betta, and why wild bettas are Vulnerable.
Recommended ages: 3 to 17 · About 15 minutes
Talk about it
- Why might breathing air be useful in a puddle or a rice paddy on a hot day?
- Pet bettas look very different from wild ones. How did people change them?
- If a species is common as a pet, why might it still need protecting in the wild?
Try at home or in class
- Blow bubbles through a straw into a cup of slightly soapy water to make a 'bubble nest', and talk about why a betta dad keeps eggs at the surface.
- Look at photos of wild and pet bettas side by side and list the differences in color and fins.
Key vocabulary: labyrinth organ, bubble nest, display, domesticated, selective breeding, rice paddy
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)
- Betta splendens (Pla Kud), 2011 assessment , IUCN Red List of Threatened Species
- FA212: Evolution, Culture, and Care for Betta splendens , University of Florida IFAS Extension
- Genomic consequences of domestication of the Siamese fighting fish (preprint, 2021) , bioRxiv
- Betta splendens, Siamese fighting fish: summary , FishBase
- Betta splendens , Animal Diversity Web, University of Michigan
- 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.