Complete Koi Betta Guide (Tank, Breeding, Diet, Care)

Koi Bettas are beautiful fish that make interesting pets. They come in all the colors of the rainbow and require minimal care. These little fish have been around for a long time and are known for their spars and attitude.

We’re going to tell you everything you need to know about Koi Bettas. We’ll begin by looking at their origin and history, what the differences are between males and females and across different varieties, and then delve into how to take care of these magnificent fish.

Table of Contents

About Koi Bettas

Koi Bettas are also known as Siamese Fighting Fish (Betta Splendens). They come from the Gourami family of freshwater fish, which have a labyrinth organ they use to breathe oxygen from the surface with. 

Koi Bettas come from stagnant swamps and rice paddies in Southeast Asia from countries such as Thailand and Vietnam. Since their native climate is hot, they like warmer water.

Keeping Koi Bettas started in Thailand more than 150 years ago. Children would collect them and put them together to watch them spar. Contests and betting on different fish soon became popular too.

They were first imported into the West in the 1890s. Today they are a popular fish to keep at home, and you can even order them online with next-day delivery available in some places! 

What Do Koi Bettas Look Like?

Wild Betta fish look nothing like the beautiful Siamese Fighting Fish we know today and are a dull gray-green with short fins. Over the years, selective breeding took place, and now Koi Bettas come in an array of gorgeous colors and fin types. 

There are seven color patterns associated with Koi Bettas: Marble, Candy, Fancy, Galaxy, Samurai, Nemo, and Tiger. They all have a mixed color effect, so that they have speckled colors on their bodies and fins. 

What Do Male Koi Bettas Look Like?

Males have bulkier bodies and curved heads. Their ventral fins are also longer and wider, and their other fins are typically longer than females too. Males have more intense colorings and patterns than females. 

Male Koi Galaxy Bettas

Male Koi Galaxy Bettas have large blue patches, along with different colorings that they sport. As with all Koi Betta varieties, the males will have brighter colors and longer ventral fins.

Male Koi Plakat Bettas

Male Koi Plakat Bettas usually come with varying shades of red alongside bold stripes of other colors. The tail fin is the shape of a fan or semi-circle. 

What Do Female Koi Bettas Look Like?

Females are generally slender and narrower, but their length can be the same as males. Females will also develop an ovipositor (egg spot) when they are old enough. This looks like a white lump which you will see form between the two ventral fins. 

Female Koi Galaxy Bettas

Female Koi Galaxy Bettas have large blue patches, along with different colorings that they sport; however, they won’t be as bright as the males of the species. The females will also have shorter ventral fins than male Koi Galaxy Bettas.

Female Koi Plakat Bettas

Like their male counterparts, female Koi Plakat Bettas usually come with varying shades of red alongside stripes of other colors, although they won’t be as bold as the male colorings. The tail fin is the shape of a fan or semi-circle. 

What’s The Difference Between A Koi Betta And A Marble Betta?

Koi Bettas actually originated from Marble Bettas and have very little difference as a result. They have slightly different genes and DNA. 

The main difference between them is their coloring. The Marble Betta should ideally have half light and half dark shadings on their bodies and fins. Koi Bettas have more than two colors and often resemble Koi fish, usually with some red and black. 

How Do You Care For A Koi Betta?

There are a number of ways to care for your Koi Betta and ensure they are happy and healthy and enjoy a full lifespan. 

Feeding And Diet

As carnivores, Koi Bettas require high-protein, high-fiber fish food. Be sure to feed your fish regularly at the same time each day if possible. This allows the fish to build a stable routine and a healthy appetite. It also removes the stressor that can occur from irregular feeding times. Never overfeed your fish, as this can cause health issues. 

Good Water Quality

Your fish will require a stable water temperature between 76-84°F and a pH level between 6.0 and 7.0. Use a sponge filter to provide some movement in the water, but be careful not to provide a strong current as Koi Bettas struggle when blown all over the tank space. 

Physical And Mental Health

Use a larger tank and promote a healthy habitat by using decorations and live plants in the tank. This will give your fish some peaceful spaces to rest and hide, and live plants will also remove harmful nitrates while promoting healthy oxygen levels in the water. 

Your Koi Betta will be an active and curious creature and requires regular mental stimulation, so adding a compatible tank mate and decorations within the tank will also improve their mental health. You can also teach your fish some tricks, such as taking food from your fingers when held close to the water line during feeding time.

Disease And Stress-Free

Poor water quality is the leading cause of stress for your Koi Betta. Prolonged exposure to stressors also leads to diseases that can cause your fish to become unhealthy. Build-ups of bacteria, algae, and other parasites will also reduce the lifespan of your fish and can be easily avoided with proper water care and maintenance. 

What Are The Best Water Parameters For Koi Bettas

While Koi Bettas are resilient to a range of water conditions and are quite easy to care for, there are some key parameters that will ensure your fish lives a healthy and happy life. 


Always try to maintain a steady water temperature between 76-84°F. Avoid heating up or cooling the water too rapidly as this will be a stressor for your fish.


Check pH levels once a week and maintain a pH level between 6.0 and 7.0 to ensure the healthiest habitat for your Koi Betta.

Water Hardness

A good water filter such as a sponge filter will help remove the hardness of the water. Be careful not to create strong currents in the water, and use a lot of live plants to promote oxygenation of the water. 

Ammonia, Nitrites, And Nitrates

You’ll need to give yourself six weeks to get your levels right. You are looking for trace levels of ammonia and nitrites and high for nitrates.

Once you have your fish in the tank, test your water weekly to make sure you have the right levels. Cycle the water once a month, performing a 50-70% water change too.

What Diet Should A Koi Betta Have?

Koi Bettas are carnivorous and require a diverse, high-protein, high-fiber diet. There are plenty of different feeds available, from pellets, frozen foods, and freeze-dried foods to live blood worms or insects, and all work well as a regular food source. 

Whatever type of food you choose to feed your fish, ensure that real proteins such as whole fish, worms, insects, or crustaceans, are included as one of the main ingredients. 

It’s always important not to overfeed your fish, and using a pellet feed is a great way to control feeding amounts. Mature fish should be fed once or twice daily at separate intervals.

You’ll know your fish has enough as there will be a slight bulge in their belly, but it should not be too extended. The fish’s belly should return to normal size by the next feeding time.  

Koi Bettas can be fussy eaters, with some preferring flakes or pellets or frozen, dried foods. Try different foods and change up the feeding process occasionally, providing food that floats or sinks to engage and excite your fish during feeding time.

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How Can You Tell Your Koi Betta Is Happy And Healthy

Koi Bettas are always healthiest when they display strong, vibrant colors. They will also display smooth swimming motions while being quite active during the day with a strong appetite. 

The Most Common Signs That Your Koi Betta Is Happy And Healthy Are:

  • Strong vibrant colors 
  • Active swimming throughout the tank
  • A good appetite and feeding habits
  • Strong fins with smooth movements while swimming


Koi Bettas will have a diverse range of personality traits. Some will be far more active, sleeping rarely during the day, while others will appear lazier and nap during the day. Some Bettas will be more aggressive, while others will flair their colors and dazzling fins with ease and appear more relaxed. 

Some Tell-tale Signs That Your Fish Is Unhealthy Include:

  • Poor appetite
  • Difficulty swimming or lethargy
  • Hiding or darting in the tank
  • Clamped of poor condition of the fins
  • Faded color 

How Long Do Koi Bettas Live & How To Improve Their Lifespan

A happy and healthy Koi Betta will have a lifespan of 2-3 years in captivity, and some Betta owners have even had fish reaching 8 or 9 years of age, although this is rare. 

If you’re purchasing your Koi Betta from a breeder or pet store, be sure to ask how old they are, as the biggest and brightest Koi Betta in the tank is likely already mature and at least 7 months old.

Maintain A Healthy Habitat

Caring for your Koi Betta and maintaining a healthy habitat will also go a long way to improving your fish’s lifespan. Koi Bettas are happiest with a tank size over 5 gallons and can withstand a range of temperatures, although they will always thrive in a water temperature of 76-84°F and pH levels between 6.0 and 7.0. 

Feeding, Cleaning, and Maintenance

Keep your Koi Betta happy and healthy by regularly changing the water and providing your fish with high-protein, high-fiber fish food. Using live plants and even tank mates such as snails will also help clean algae, provide oxygen and keep the water clean.  

Using a sponge filter will also improve oxygen levels in the water and promote a longer lifespan for your fish. Always make sure you administer quick treatment should you notice any symptoms of a disease. 

Keep Your Koi Betta Stress Free

Koi Bettas are highly sensitive to stress and will live far longer if they are not constantly exposed to perceived threats. They also like some privacy and places to hide, so adding decorations to your tank will provide a peaceful sanctuary if they are ever scared or threatened. 

Never overcrowd your tank with decorations or other tank mates, and always check that tank mates are compatible. 

What Size Tank Do Koi Bettas Need?

Koi Bettas are resilient to small tanks and can live in a small tank of no less than 2 gallons. While these small desktop tanks are OK, it’s always better to have a larger tank of at least 5 gallons, especially when you are adding large amounts of tank decorations or large numbers of tank mates (say 4 or more fish).

If you’re using a small tank, ensure that there is enough decoration for the fish to be able to comfortably hide without overcrowding the tank. If you’re planning to have a group of Koi Bettas, start off with a 10-gallon tank and allow 2-3 gallons in size per additional fish. 

A larger tank of over 5 gallons is always better, no matter how many fish you are planning to have. Koi Bettas are inquisitive by nature and like to be able to roam and peacefully hide within small nooks and decorations in the tank. Overcrowding will cause undue stress on your fish and may cause more aggressive behavior, particularly between your Koi Betta and other tank mates. 

Ideally, you’ll want enough decoration, so the fish are not constantly in the direct eye-line of one another. Using rocks and live plants is a great way to create a healthy environment that will promote the longevity of your fish.

What Are Common Diseases That Affect Koi Bettas?

While Koi Bettas are highly resilient to differing water temperatures, there are some typical diseases that affect the Koi Betta species. Following the proper care guides for your fish will keep them colorful and energized, and if you notice any symptoms of illness, it is always best to be proactive. 

Some tell-tale signs that your Koi Betta is sick are:

  • Lethargic behavior
  • Loss of appetite for extended periods (more than 1-2 days)
  • Fading of color 
  • Damaged or clamped fins
  • Difficulty breathing or gasping

There are a number of diseases that are prevalent and will leave your Koi Betta with poor health. The causes range from poor water conditions, bacteria or parasites in the water to high-stress environments, overfeeding, or poor nutrition. 


A symptom of Columnaris is white cotton-like growth along the fins and gills. The cause is likely due to poor water quality or stress due to overcrowding of your tank. If you notice any symptoms, be sure to clean your tank and add an antifungal medication to the clean tank water. 


This is one of the most common diseases that will lead to the poor health of your Koi Betta. Symptoms include swelling of the body and raised scales. The cause is often due to a virus or bacterial infection in the water and can be treated using Kanamycin Sulfate or Maracyn II products which are available from your local pet store or easily purchased online. 

Fin And Tail Rot (Pseudomonas Fluorescens Bacteria)

If you notice that the fins or tail of your Koi Betta are frequently damaged or in poor condition or turning black, you’ll need to improve the water quality, and it can be treated using aquarium salt. More severe cases require a bacterial water treatment such as Maracyn II antibiotics or Kanaplex. 

Also, check that the tank mates are not attacking the fins or tail of your Koi Betta, as multiple aggressive fish are not suitable companions.


This disease causes the eyes of your Koi Betta to bulge or extrude from the head of the fish and is caused due to prolonged exposure to poor water quality or Tuberculosis. If you see any symptoms, thoroughly clean the water and use either Maracyn II antibiotic or Kanaplex. 

Ich/Ick/​​Ichthyophthirius Multifiliis

Often caused by poor water quality, stress, or introducing a contagious tank mate, Ich can be identified by small white dots that will appear on the body, fins, or gills. You may also notice that your Koi Betta will rub against the tank or other objects. 

This disease is often fatal, so administering treatment quickly is crucial. Increase the temperature of the water up to around 81-86°F, then administer specialized ich removal medicine that contains malachite green and formalin ingredients. You’ll need to cycle the water daily, gradually diluting the medicine each day to remove the disease from the tank. 

Swim Bladder Disease

Swim Bladder Disease makes your fish have difficulty swimming or maintaining a regular depth in the tank. It may also cause your fish to swim on its side. The disease is often caused by overfeeding, poor nutrition, shock or stress, or a parasite infection in the water. 

Although rarely fatal, this disease causes great discomfort to your fish and should be treated quickly. Treatment does vary depending on the cause; however, overfeeding is one of the most common causes and requires 2-3 days of fasting to allow for recovery. 

If the cause is not obvious, it is worth cleaning the tank and applying an all-purpose fish antibiotic such as Maracyn II. 

How Do You Breed Koi Bettas?

Koi Bettas breed most successfully when they are young, ideally between 4-12 months and only up to around 14 months. This will ensure the healthiest fry with the best genetics and the greatest chance of survival. 

Choosing The Right Breeding Pair

You’ll want to consider the breeding pair and ensure you select the fish from a reputable breeder. If you’ve bought your Koi Betta from a pet shop, monitor your fish over a few weeks and find the most dominant female to pair with the male. 

You’ll also want to choose a male that does not show any sign of lethargy or disease. If buying from a pet shop, choose the make that has the brightest colors and the most elaborate fins. Males that are red in color are also more attractive to female Koi Bettas.   

Create A Separate Breeder Tank

If you’re looking to breed your Koi Betta, you’ll need to set up some specific equipment and monitor the fish carefully during spawning season. You’ll need two tanks, with one tank dedicated as your breeder tank. 

The breeder tank should be filled with around 3-5 inches of water, and this will allow the fry to easily reach the surface. Make sure you have plenty of decoration in the tank as Koi Bettas like privacy when they mate. 

Monitor Tank Conditions

Monitor the water conditions of the breeder tank and keep the water temperature and pH levels the same as the main tank. A water temp of 76-84°F is ideal, and it’s best to maintain the pH level between 6.0-7.0. Use a sponge filter and water heater to ensure your tank has the best conditions for breeding.

Introduce Your Koi Bettas To The New Breeder Tank

It is also important to allow your male and female Koi Bettas to settle into the new breeder tank environment, giving them around 2-3 weeks to feel at home. If they are stressed or have too many distractions, they may not mate. 

First, introduce the female to the tank and allow at least an hour before introducing the male. It may also be worth adding a divider to the tank so each fish can settle into its environment privately. If you’re adding the male to the tank directly with the female and without a divider, add the male to the opposite end of the tank, away from the female. 

Once the male is introduced to the tank, he will flair his fins and display more vivid colors. The female will reciprocate and will display her vertical “barring” pattern when ready for mating. 

Once the female has signaled she is ready, the male will build a bubble nest, and upon approval of the nest from the female, the mating process will begin. You will likely see a lot of chasing and biting, and this is considered normal and may last around 4-6 hours. Closely monitor the situation, and add some decoration such as Christmas Moss if the female looks exhausted. 

If at any time you’re concerned about the welfare of the female fish, it is best to remove her from the tank as the constant chasing and biting from the male can overwhelm the female fish. 

Mating Your Koi Bettas

You’ll notice several tight embraces between the male and the female where she will slowly start to release eggs during each embrace. The female will enter a slight sleep-like state during the release of eggs, often appearing dead and floating sideways, and this is totally normal. The male will now scoop the eggs and start to place them into the bubble nest one by one. 

From this point onwards, for the next day or two, the male will monitor and maintain the nest, blowing more bubbles onto them as he needs to. 

Keeping the tank slightly humid will aid the hatching of the eggs and the heat provides welcome conditions for the development of the fry once hatched. The easiest way to create more humidity is to cover the top of the tank with some plastic wrap during the mating phase. 

Hatching The Fry

You’ll notice your Koi Betta fry start to hatch and fall from the bubble nest. The male will dart around below and scoop them up and try to return them to the nest. This process will repeat over and over and eventually, the small fry will start to swim freely, slowly taking a horizontal swimming position.

What Tank Mates Can Live With Koi Bettas

Although Koi Bettas are better known as solitary and aggressive fish, there’re plenty of tank mates that will happily live in the same tank as your Koi Betta, or even amongst a group within a female-only sorority.

Koi Bettas can happily live alone or coexist with other tank mates, but either way, it’s important to understand the temperament and personality of your fish before introducing new tank mates. 

Never introduce other aggressive fish to the tank, as this will aggravate your Koi Betta and will lead to stress and confrontation. Always quarantine any new fish in a separate tank for 4-6 weeks, and be sure to monitor tank mates closely for the first 3-4 days. 

If you notice your Koi Betta is under constant stress, it will likely have poor health and may die if crowded with too many tank mates or other highly aggressive fish. It may also attack the other fish. Using a clear divider in the same tank will help climatize new additions to the tank. 

Here are some great tank mates for Koi Bettas and also a few fish that you may want to avoid.

Snails/Pomacea Bridgesii

Introducing snails such as the commonly known Apple Snail (also known as the Mystery Snail) to your tank is a win-win for you and your Koi Betta. The snails will clean the tank and remove algae as they roam, and your Koi Betta will mostly ignore the snail due to their docile nature and incredibly slow movement. 

Feeder Guppies/Poecilia Reticulata

The highly common Feeder Guppies also make great tank mates for your Koi Betta. They do not have overly bright colors or extravagant fins and typically grow to just over an inch long. They are easy to care for and also thrive in the same pH, water temperatures, and conditions that are suited to a tank with Koi Bettas. 

Cory Catfish/Corydoras

Corydoras have an easy temperament and are non-aggressive, living on the bottom and feeding on algae, making them a great addition to your tank community with your Koi Betta. They can live alone or in schools, and it’s recommended that a small school of 4 or more will live harmoniously with your Koi Betta. 

Clown Plecos/Panaque Maccus, Dwarf Loricariid

This bottom-dweller is a great tank mate for your Koi Betta due to its relaxed temperament and size. The Clown Plecos grows up to 4 inches long, is easy to care for, and has tough skin that will be resistant to attacks from other fish. 

Marimo/Moss Ball

Another ideal tank mate for your Koi Betta is Marimo (also known as the Cladophora ball) which is a living plant that looks a lot like a moss-covered tennis ball. 

They are very easy to care for and can live up to 100 years, growing less than 0.2 inches each year. They are great tank mates as they are algae and nitrate eaters and are excellent for oxygen production, keeping your tank and Koi Bettas happy and healthy. 


How Much Do Koi Bettas Cost

Expect to pay around $20-50 per fish, depending on the sex, coloration, and fin size of the fish. Males are slightly more expensive than females, largely due to their more striking jewel-like appearance and more elaborately colored fins. 

Your typical retail fish shop will likely have a variety of fish available that will vary in price depending on what breeding line, coloring, and size of the fins you choose. Alternatively, you could even order a Koi Betta online (depending on where you live), with many different colorations of fish available online with free delivery.

Are Koi Bettas Aggressive?

Yes, male and female Koi Bettas are aggressive by nature and have been bred over the years to viciously attack other fish in the same environment or tank space. This will often result in one or both of the fish dying from the attacks.

The male Koi Betta is far more aggressive than the female and will be intolerant to any other fish of a similar size or color that they see as a threat to their dominance. Female Koi Bettas are far less aggressive to one another and other fish species, and with the right tank size and decorations can even exist together. 

Can You Put Koi Bettas Together?

The males are particularly aggressive and you should never pair them together in the same tank. Male Koi Bettas will viciously attack any other male Koi Betta that is within the same tank, and on occasion, may also attack a female if the female is also aggressive. 

Female Koi Bettas can live together in groups (often referred to as Betta sororities) and introducing one male for every 4-6 females is a good way to ensure that the male does not pester one female betta to death during spawning. A good way to improve the chances of your Koi Betta fish coexisting is to use a large tank of around 20 gallons. 

How Big Do Koi Bettas Get? 

Koi Bettas do not grow to become overly large in size and will usually grow to a maximum of 3 inches (7.6 cm) in length once mature. For a Koi Betta to reach its mature size, it will take around 7 months. 

Koi Bettas are usually a short-tailed variation, with small fins and the males will typically have more ornate and slightly larger fins than females. 

About the author

Hey there! I'm Antonio, the passionate owner and chief editor of Betta Care Fish Guide. With over half a decade of hands-on experience, I've become your go-to expert for all things betta and tropical fish.

Over the past 5 years, I've not only kept bettas and other tropical fish but also connected with a diverse network of hobbyists, seasoned fishkeepers, and even veterinarians.

Now, I want to help other beginner fish keepers who had the same questions as me when they were just starting out! So they can save themselves a ton of time and keep their fish happy and healthy!