A koi betta is a marble betta, and the pattern is a gene that moves
Koi betta fish are Betta splendens with a pattern, and the pattern is unusual in that it does not stay put. Both our koi sources describe the cause the same way and neither uses the word color: it is a gene that changes position in the genome.
Aquariadise puts the relationship first: the koi betta is a variation of Betta splendens, otherwise known as the Siamese fighting fish, with striking patterns that resemble that of a typical koi fish, and koi bettas are a specific variation of marble bettas. So koi is a subset, not a separate thing, and any page about marble bettas is also a page about this fish.
The mechanism is the part worth reading twice. Aquariadise: marble variations are due to selective breeding which causes jumping genes, also known as transposons. These jumping genes are pieces of DNA that can actively move around to different parts of the genome within an individual cell, simply meaning that at any given time, these fish can change to a new color or increase pigment intensity. Aquarium Store Depot gives the same thing in one line: the mutation is a jumping gene, a DNA sequence that can change its position within the genome.
Two independent sources naming the same molecular mechanism is rare on this site. Six other pages here discuss selective breeding, including our female betta fish guide and our guppy, corydoras and cherry shrimp records. None of them names a transposon. This is the only page here where the trait a buyer is paying for is explained down to the DNA.
What this guide is
- The question
- Three thousand five hundred searches a month for a pattern, and a pattern cannot change how a fish is kept. Our sources changed three care rows anyway.
- Why it is filed here
- Under breeding, because a koi betta is a breeding outcome rather than a species, and one source dates it to a failed attempt at something else.
- The record behind it
- Our betta record, the only Betta splendens record here, whose adult size and diet rows both disagree with the koi pages.
The pattern changed three care rows, which is three more than a pattern can change
A koi betta is the same species as any other betta. So the figures on a koi betta page and the figures on a Betta splendens page should be identical, and they are not. This is every number our four sources publish, with our own record in the last column.
| Figure | Aquariadise, koi | Store Depot, koi | Seriously Fish, species | This site |
|---|---|---|---|---|
| Tank | 5 gal | 5 gal | 45 by 30 cm, about 11 gal | 5 to 10 gal |
| Temperature | 77 to 83 °F | 76 to 80 °F | 72 to 86 °F | Around 80 °F |
| pH | 6.5 to 7.5 | 7 | 6.0 to 8.0 | 6.0 to 8.0 |
| Hardness | none | soft water | 1 to 15 dGH | 18 to 268 ppm |
| Adult size | about 3 in | up to 3 in | 70 mm SL, 2.8 in | 2.4 to 2.8 in |
| Diet | Protein, live and frozen | Omnivore | Carnivorous | Carnivore |
| Lifespan | none | 2 to 3 years | none | 3 to 4 years |
The size row is the clearest one. Both koi pages say three inches. Seriously Fish gives a maximum standard length of 70 mm, which is 2.8 inches, and our betta record publishes 2.4 to 2.8 from its own sources. Three inches is not a koi betta figure, because there is no such thing as a koi betta figure. It is a rounded-up betta figure, and the rounding travels with the pattern.
The diet row is the one that would change what you buy. Store Depot types the koi betta as an omnivore and says pellet betta fish food at minimum. Seriously Fish calls the species carnivorous and names Daphnia, Artemia or chironomid larvae, bloodworm, plus small insects. Our record says Carnivore. Thirteen records on this site carry Omnivore and four carry Carnivore, and the betta is one of the four, so this is not a loose word on our side.
The tank row moves in the opposite direction from the other two, which is worth pausing on. Both koi pages give 5 gallons, the figure most shops give. Seriously Fish asks for a base of 45 by 30 cm for a single male or a pair, which is about 11 US gallons, just above the ceiling of our own record’s 5 to 10. Nine records here sit at 5 gallons and the betta is one of them, so 5 is a real floor rather than a shop number, but the species reference wants double it.
The lifespan row is a straight contradiction with our own page. Store Depot gives 2 to 3 years; our record gives 3 to 4, and Aquariadise and Seriously Fish publish nothing. The two figures meet at a single year and share nothing else. On this site 2 to 3 years is the figure our guppy, amano shrimp and rabbit snail records carry, and 3 to 4 belongs to the betta alone.
One row does agree exactly, and it is the one nobody checks. Our record’s hardness of 18 to 268 ppm is Seriously Fish’s 1 to 15 dGH converted, to the round number. Where our sources and the species reference are working from the same measurement, they land on the same figure; where the koi pages are working from the pattern, they do not.
Six named types, and a fish that may not stay any of them
| Name | Named by | What it describes | Its own care figures |
|---|---|---|---|
| Fancy | Store Depot | At minimum three different colors | none |
| Galaxy | Store Depot | Iridescent scaling that shimmers when moving | none |
| Candy | Store Depot | Black, red, blue or yellow, like a candy treat | none |
| Tiger | Store Depot | A yellow body with black or blue to complement it | none |
| Nemo Palkat | Store Depot | Orange, red and black; the second most popular. Plakat is a tail shape, so this name mixes the two axes | none |
| Samurai | Store Depot | Dragon scaling with the marble; called the rarest of the six | none |
| Marble | Co-Op, Aquariadise | The parent pattern and the gene behind all six | none |
| Halfmoon, crowntail, plakat, doubletail, veiltail | Co-Op | Tail shape, not pattern, and pairs with any of the above | none |
| Elephant ear or dumbo | Co-Op | Enlarged pectoral fins, prone to splitting | none |
Store Depot names six: Fancy, Galaxy, Candy, Tiger, Nemo Palkat, Samurai. These are trade names for arrangements of the same marble pattern rather than lines with separate care, and no source we hold publishes a single different figure for any of them.
It also dates the fish, and the origin is an accident: koi bettas were born from a failed attempt at trying to create the first butterfly black betta. The name is purely descriptive, because the Betta’s colors and shine resemble that of Koi fish.
Aquarium Co-Op has a page on betta types and never uses the word koi. What it describes instead is the parent pattern: a marble betta has an evenly distributed pattern of high contrast dots, splotches, or patches that ideally covers the entire body, and the marble gene can cause a betta fish to have completely different color patterns over the course of its development from juvenile to adulthood. Its list of forms is seven, and they are shapes rather than patterns: halfmoon, crowntail, plakat, doubletail, veiltail, elephant ear and alien betta.
So the buying problem writes itself, and both sources state the mechanism without quite stating the consequence. Store Depot on the patterns: those patterns change. Constantly. Co-Op: the gene can produce completely different patterns between juvenile and adult. The fish in the cup is not a promise about the fish you will own, and no source we hold says how long the pattern takes to settle or whether it settles at all.
That is a real gap rather than a hedge. A buyer choosing between two cups is choosing between two present states of a trait that is defined by not holding still, and the six trade names above are names for present states. This guide cannot tell you which one your fish will keep, because none of our four sources publishes it.
On breeding for a pattern, Store Depot is honest about the odds: the fish is easy to breed but crossing two marble bettas yields unpredictable results. That is what a transposon means in practice, and it is the same sentence as the buying problem seen from the other end.
The water, the fins, and the four ways one source separates a male from a female
The water is the easy part of a koi betta and our sources agree across all of it. Store Depot asks for 76 to 80 °F, a pH of 7 and soft water; Aquariadise asks for 77 to 83 °F and pH 6.5 to 7.5 in a heated tank. Both sit inside our betta record’s published pH of 6.0 to 8.0, and both require a heater, which is the opposite of our celestial pearl danio record where two sources argue for no heater at all.
On maintenance Store Depot gives the only water schedule any source we hold publishes for this fish: make sure you change the water at least twice a month. On the filter it names the trade-off rather than a product: a sponge filter can work great, but may not provide enough filtration in a full planted setup. On substrate: gravel and sand are the best substrate choices for koi bettas.
Plants are asked for by function rather than by name. Store Depot: provide many plants which your fish can use as hiding or sleeping spots. Neither koi source names a plant species, so that choice comes from elsewhere on this site: our java fern, anubias and java moss records all publish temperature bands that contain a betta tank, and all three are low light plants that need no injected CO2.
The colors are where the six names in station 03 actually live, and Store Depot describes each one by pigment rather than by shape. The Fancy shows at minimum 3 difference colors; the Galaxy takes its name from iridescent scaling that shimmer when they are moving; the Candy is black, red, blue or yellow and named for looking like a candy treat; the Tiger has a striking yellow body with black or blue colors to compliment it; the Nemo is orange red and blacks and the second most popular; and the Samurai, called the rarest, has the desired dragon scaling with the marble.
Read that list against Aquarium Co-Op’s and the two are describing different axes of the same fish. Co-Op’s seven forms are tail and fin shapes, halfmoon, crowntail, plakat, doubletail, veiltail, elephant ear and the alien betta, and it notes the elephant ear form can be paired with all sorts of different tail types and color patterns, while those delicate pectoral fins can be prone to splitting. So a koi betta carries a pattern from one list and a fin shape from the other, and one of Store Depot’s six names, the Nemo Palkat, quietly takes one from each.
Sexing is the one row where Store Depot is more detailed than any other source we hold on any betta page, and it gives four separate tells. Female betta fish tend to have smaller fins, by which we mean thinner and sometimes shorter fins, than their male counterparts. The physique of the female betta fish is more streamlined than the male koi betta. Male koi betta have larger heads than females, and they have a curved shape which makes their body appear bulky. And the one that settles it: you can also look for an egg spot, white lump, which adult female betta fish develop near their ventral fins.
Our female betta fish guide carries the stocking half of that, because a female betta is a different stocking problem rather than a different fish. What no source we hold covers for a koi betta is disease. Store Depot addresses no health problem at all, and Aquariadise gets closest by describing a lump as the result of superficial abrasions, bacterial infections, or ulcers, which is a symptom rather than a list.
What selective breeding did change, and it is not the pattern
The argument of this guide so far is that a pattern cannot change care. That is true of the pattern and not true of the domestication behind it, and Seriously Fish says so in one sentence: ornamental strains seem to be more aggressive than any other Betta species. More aggressive than the wild form of its own species, and more aggressive than its wild relatives.
It adds the two facts that follow from a century of line breeding. The wild form is rarely seen in the aquarium hobby, and mass-produced strains often show health problems. So the fish in the shop is a domesticated animal in the strict sense, and a koi betta is one of the more heavily selected versions of it.
That is where the aggression rows on this site come from, and they are the rows that actually decide a tank. Our betta record and our betta fish tank mates guide carry them, and Aquariadise gives the flat version here: never place two male betta fish in the same tank.
Aquariadise also gives the figure that separates a betta in a jar from a betta in a community, and it is not 5 gallons. For a mixed species tank, a minimum tank size of 15 gallons, 56.8 L, is recommended. That is triple the number on the same page for the fish alone, and it is the honest answer to the most common follow-up question about any betta.
One last line from Seriously Fish belongs on a page about a bred pattern, because it is the cost of the trade rather than a fact about the tank. Habitat loss or modification across its natural range has increased significantly, and introduced ornamental forms harm the genetic integrity of wild populations. The wild Betta splendens and the fish named after a carp are the same species on paper and no longer the same animal in practice.
None of this changes a single row in the table in station 02. It changes what the rows are for: a koi betta is not a harder fish than a betta, it is a betta whose ancestors were selected hard enough that the species reference now flags temperament and health as consequences.
What it costs, and where that sits among the three other prices on this site
Store Depot is the only source we hold that publishes a price, and it is a wide one: the fish can go up to $65 apiece, with the lowest price being around $30. For a fish whose care rows are identical to a five dollar betta, that is the whole commercial point of the pattern.
This site rarely prints a price, and it prints one when the number is the story. Three other pages here carry a dollar figure: our flowerhorn record at $600, our discus record at $300, and our tetra fish guide at $1 to $4. So a koi betta at $30 to $65 sits an order of magnitude above the tetra and an order below the flowerhorn.
What the price buys is worth stating plainly, because the table in station 02 already answered it. It buys a present arrangement of pigment on a fish that our sources agree will rearrange it. It does not buy a larger fish, a longer-lived fish or an easier one, and on two of those three our koi sources print figures that suggest otherwise.
Store Depot names the tank mates it would accept, and every group it names has a record here: tetras, cherry barbs, freshwater shrimp, corydoras and snails, with cichlids and aggressive species to avoid. On this site freshwater shrimp means our cherry shrimp, amano shrimp and ghost shrimp records, and our betta fish tank mates guide prints each overlap and each refusal rather than a list.
Koi betta fish questions, answered from the sources
What is a koi betta fish?
A Betta splendens with a marble pattern that resembles a koi carp. Aquariadise: the koi betta is a variation of Betta splendens, otherwise known as the Siamese fighting fish, with striking patterns that resemble that of a typical koi fish, and koi bettas are a specific variation of marble bettas. It is not a separate species, a hybrid, or a size class, so its care is the care on our betta record.
Do koi bettas change color?
Yes, and that is the definition rather than a defect. Aquarium Store Depot on the patterns: those patterns change. Constantly. Aquarium Co-Op: the marble gene can cause a betta fish to have completely different color patterns over the course of its development from juvenile to adulthood. The cause is a jumping gene, and no source we hold says how long the pattern takes to settle or whether it settles at all.
Why do koi bettas change color?
Because the gene responsible physically moves. Aquariadise names it: marble variations come from jumping genes, also known as transposons. These jumping genes are pieces of DNA that can actively move around to different parts of the genome within an individual cell, simply meaning that at any given time, these fish can change to a new color or increase pigment intensity. Store Depot agrees: the mutation is a jumping gene, a DNA sequence that can change its position within the genome.
What size tank does a koi betta need?
Both koi sources say 5 gallons and the species reference asks for about eleven. Aquariadise: at least a 5 gallon heated tank. Store Depot: 5 gallons. Seriously Fish asks for a base of 45 by 30 cm for a single male or pair, which is roughly 11 US gallons and just above the ceiling of our own betta record’s 5 to 10. For a community tank Aquariadise triples its own figure: a minimum tank size of 15 gallons, 56.8 L, is recommended.
How big do koi bettas get?
Three inches on both koi pages, 2.8 on the species reference. Seriously Fish gives a maximum standard length of 70 mm, and standard length stops at the base of the tail. Our betta record publishes 2.4 to 2.8 inches. A koi betta is the same species as every other betta, so the extra two tenths of an inch is a rounding that travels with the pattern rather than a fact about the fish.
How long do koi bettas live?
Our two sources disagree and they meet at one year. Store Depot gives 2 to 3 years. Our betta record gives 3 to 4 from its own sources. Aquariadise and Seriously Fish publish no lifespan at all. Nothing about a color pattern should move this row, which is exactly why the disagreement is worth printing.
What do koi bettas eat?
Our sources contradict each other on the diet type, not just the food. Store Depot calls the koi betta an omnivore and accepts pellet betta fish food at minimum. Seriously Fish calls the species carnivorous and names Daphnia, Artemia or chironomid larvae, bloodworm. Aquariadise asks for protein and low fillers, with live and frozen foods, such as brine shrimp and bloodworms, a couple of times a week. Our betta record says Carnivore.
How much does a koi betta cost?
Store Depot is the only source we hold with a figure: up to $65 apiece, with the lowest price being around $30. For context, three other pages on this site carry a price, our flowerhorn record at $600, our discus record at $300 and our tetra fish guide at $1 to $4. What the money buys is a present arrangement of pigment on a fish our sources agree will rearrange it.
What are the types of koi betta?
Store Depot names six: Fancy, Galaxy, Candy, Tiger, Nemo Palkat, Samurai. These are trade names for arrangements of the same marble pattern, and no source we hold publishes a single different care figure for any of them. Aquarium Co-Op’s betta types page lists seven forms instead, and those are shapes rather than patterns: halfmoon, crowntail, plakat, doubletail, veiltail, elephant ear and the alien betta.
Is a koi betta harder to keep than a normal betta?
No, and no source we hold suggests it is. Every care figure our sources publish for a koi betta is a Betta splendens figure, and where they differ from the species reference they differ in the generous direction rather than the demanding one. What is harder is the domestication behind it: Seriously Fish notes that ornamental strains seem to be more aggressive than any other Betta species and that mass-produced strains often show health problems.
Are koi bettas aggressive?
As aggressive as any other betta, which Seriously Fish rates above the wild form and above its wild relatives: ornamental strains seem to be more aggressive than any other Betta species. Aquariadise gives the rule without conditions: never place two male betta fish in the same tank. Our betta fish tank mates guide prints each pairing with its overlap and its refusal.
What can live with a koi betta?
Store Depot names tetras, cherry barbs, freshwater shrimp, corydoras and snails, and says to avoid cichlids and aggressive species. Every group it names has a record here: our tetra fish guide, corydoras record, and for shrimp our cherry shrimp, amano shrimp and ghost shrimp records. Aquariadise adds the figure that makes it possible: 15 gallons rather than 5.
Can you breed koi bettas?
Yes, and you cannot breed the pattern reliably. Store Depot calls the fish easy to breed and says crossing two marble bettas yields unpredictable results. That is what a transposon means at the tank level: the trait is defined by moving, so it does not segregate cleanly. Store Depot also dates the whole variety to an accident, saying koi bettas were born from a failed attempt at trying to create the first butterfly black betta.
Is my koi betta losing color because it is sick?
None of our four sources answers this directly, and it is the question the marble gene invites. What they establish is that pigment change alone is expected: the gene moves and Store Depot says the patterns change constantly. What they do not give is a test for telling that apart from illness. Aquariadise discusses lumps rather than color, noting a lump may be the result of superficial abrasions, bacterial infections, or ulcers. On anything beyond pigment, treat our betta record and a vet as the sources, not a variety page.
How do you tell if a koi betta fish is male or female?
Store Depot gives four tells, and it is more detailed on this than any other source we hold on any betta page. Female betta fish tend to have smaller fins, by which we mean thinner and sometimes shorter fins, than their male counterparts. The physique of the female betta fish is more streamlined than the male koi betta. Male koi betta have larger heads than females, and they have a curved shape which makes their body appear bulky. And the definitive one: you can also look for an egg spot, white lump, which adult female betta fish develop near their ventral fins. Our female betta fish guide has the stocking side.
What plants and substrate does a koi betta fish tank need?
Plants by function, substrate by name. Store Depot: provide many plants which your fish can use as hiding or sleeping spots, and gravel and sand are the best substrate choices for koi bettas. Neither koi source names a plant species, so that choice comes from elsewhere: our java fern, anubias and java moss records all publish bands that contain a betta tank and none of the three needs injected CO2.
How often should you change the water in a koi betta fish tank?
At least twice a month, which is the only water change schedule any source we hold publishes for this fish. Store Depot also names the filter trade-off: a sponge filter can work great, but may not provide enough filtration in a full planted setup. Neither koi source gives a percentage to change or a test regime, so those figures are not on this page.
What is the difference between a koi betta and a marble betta?
A koi betta is a marble betta. Aquariadise: koi bettas are a specific variation of marble bettas. Marble is the pattern class and the gene; koi is the subset whose blotching reads as a koi carp. That means every marble betta page applies to a koi betta, including Aquarium Co-Op’s, which describes the marble pattern in detail and never uses the word koi once.
Do koi bettas need a heater?
Yes. Every source we hold puts the range above room temperature: Aquariadise 77 to 83 °F, Store Depot 76 to 80, Seriously Fish 72 to 86 for the species, and our own betta record around 80. Aquariadise specifies a heated tank in the same breath as the 5 gallon figure. This is the opposite of our celestial pearl danio record, where two sources argue the tank should have no heater in it.