Koi Betta Fish: Complete Guide

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koi betta fish

There are many kinds of fish available these days, including betta fish. Aside from the standard kinds of Siamese fighting fish, you can now find ones with beautiful coloring. That brings us to the stunning colors of the koi betta fish. Though this particular type of betta fish has been around for a while, there is still confusion about koi betta fish.

Where do they come from? Are they a different species? Do you care for them the same way as normal betta fish?

We are going to do a deep dive today about the koi betta fish to answer all those questions and more. Let’s get started.

Quick Facts About Koi Betta Fish

The koi betta fish was created through the selective breeding of marbled betta so that it will look like a koi fish. That is why the speckling and colors have given them such a name. You will often see koi betta fish with patches of black, red, yellow, and orange, but there have been ones with pink and white fins, too.

Because of their uniqueness and selective breeding process, koi bettas are far more expensive than other betta fish breeds. Even more than marbled betta fish.

Here are some quick facts about koi betta fish to know:

Adult Size: About 3 inches
Lifespan: About 3 years
Diet: Carnivore
Temperature: 77-80.6 degrees F (25-27 degrees C)
pH Level: 6.0-8.0
Minimum Tank Size: 2.5 gallons
Care Level: Easy

Caring For Koi Betta Fish

Caring for a koi betta fish is no different from a regular betta fish. Wild betta fish are found in the rice paddies and streams of Southeast Asia, but mainly in Indonesia, Vietnam, and Thailand. Because of that, you can expect them to have naturally adapted to the weather conditions in these locations.

In other words, you want to be very careful about the temperature of the water and the quality.

koi betta fish

Koi bettas will be happiest in water between 77-80 degrees Fahrenheit, but they will be okay with 74-82 degrees, like normal betta. However, you should avoid rapid temperature fluctuations.

Keep a constant eye on the water quality, as well. The pH, nitrite and nitrate levels, and ammonia should be under control. Check these levels at least once a week. Change the water in your betta’s tank completely at least twice a month, and replace about 15 percent of the water weekly.

koi betta fish

The ideal water condition is soft with a neutral to minimally acidic pH of 6.0 to 8.0. Keep the water movement as close to their native habitat as possible—meaning “minimum” water movement. However, if you put your koi betta in a larger tank with some circulation, you can simply build calmer waters into the design of the tank. (We’ll discuss the ideal tank set up a little later.)

Most koi betta prefer planted aquariums that mimic their natural habitat. Give your betta plenty of resting and hiding spots. Live plants can also act as a source of additional nutrition, but keep in mind that betta fish are generally carnivorous.

You don’t have to worry much about providing oxygen-rich water, though. Koi betta fish have respiratory organs that let them breathe in pure air from the surface. Because of this, you should ensure they have access to the water’s surface.

Can Koi Betta Live Together?

That depends on the gender. By nature, domesticated betta fish are slightly more aggressive than their wild brethren. You can never keep two males in the same tank, because they will attack one another and never stop. Additionally, some males will be aggressive towards females when breeding or when a female gets too close to a bubble nest.

That said, you can keep betta sororities—up to five females—in a tank together. If you want a successful sorority, be sure to choose your bettas carefully and have enough space for all the bettas to swim.

Koi Betta Fish Feeding and Nutrition

In the wild, betta fish are mainly carnivorous. They will eat insects and larvae, as well as things that sometimes fall into their stream or paddy. That is why betta fish have upturned mouths—so they can catch things on the water’s surface. Because of this, the betta digestive system is geared towards meatier options.

Select foods that consist of live or frozen insects and insect larvae. You can also supplement this with flakes and pellets.

Feed your mature betta fish once or twice a day, depending on its activity levels. Keep in mind that it is very easy to overfeed betta fish, since they might learn to beg and will always be looking around for something to chew on. If you have betta fry, you should feed them three times a day.

Also, the betta’s belly can stretch. This is dangerous, especially if you feed them dried foods that can expand in water. You will know you are feeding your betta enough when the belly takes on a distinct round shape. That said, a female carrying around fertilized eggs will also have a rounded belly.

Betta Fish Is Not Eating

You should be feeding your betta fish according to a set schedule and also by the size of its stomach. If you notice that your betta isn’t eating as much and that its belly is looking permanently distended, your fishy friend might be bloated.

Wait until the bloating has receded before feeding your betta again. Also, consider giving your betta some foods high in fiber, like green peas (1 or 2 peas) to assist with digestion.

How To Tell If Your Koi Betta Fish Is Male or Female

Although you often see pet stores labeling betta fish as male or female, you should know that discerning the sex of these fish can be a challenge. Still, if you want to figure it out, then know this: You will have to wait until about 2-3 months of age. Before that, there is little sexual dimorphism present.

Determining the sex of a betta fish:

male vs female koi betta

  • Look at the ventral fins. Males have longer, wider fins while females usually have thin ventral fins.
  • Males have bulkier, thicker bodies, and their head is curved. Female bettas look more aerodynamic.
  • Males have brighter colors than females. Meanwhile, females sometimes darken or brighten their colors, depending on the outcome of breeding advances.
  • The fins on males will have a flowing quality, while females do not.
  • Generally, females have shorter fins than males, but this will also depend on the type of tail the betta fish have. Once you know what kind of tail fin the betta fish has, you will be able to figure out if you have a male or female.
  • Look for the egg spot, which looks like a white dot or lump. You can often see this between the ventral fin and the head. Younger females do not have the egg spot.

Breeding Koi Betta Fish

Any hobbyist can have a successful breeding program. All you need are a couple of healthy betta under 1 year old, a 10 gallon tank, and the perfect water temperature. You will want the water to be around 7.0 pH and close to 85 degrees Fahrenheit, since that will prompt the male betta to build a bubble nest.

Make sure you provide a safe spot for the female to hide, since the male can become aggravated during courtship.

Once the male starts making his advance, he will circle the female, flare his gills, and show off his brightest colors. If the female accepts, she will release her eggs for fertilization. Afterwards, the male will scoop up the eggs and place them into the bubble nest. From there, you should quickly remove the female, because the male betta fish will become very protective of his eggs.

Once the fry hatch, remove the male. He will often eat the young betta within 2 days of hatching.

Best Tank Set Up For Koi Betta Fish

If you plan on keeping a happy and healthy koi betta fish, then you are going to need the right tank and an ideal set up.

The best tank size for a betta fish is 5 gallons or more. Yes, you can put a betta fish in a vase or a smaller tank, but this ensures a shortened lifespan and a bored fish.

A bored betta is one that doesn’t develop quirks—and that is the best part of keeping a betta to begin with.

Therefore, if you want to see your koi betta fish in all its splendor, purchase at least a 5 gallon tank and some aquatic plants to go along with it.

Do Betta Fish Need Filters?

Yes. You will want a filter to keep the fish tank clean. Without a filter, you run the risk of exposing your koi betta fish to toxic materials and disease. Keep in mind that betta fish do not like strong currents, so you will need a gentle filter. An adjustable one is best.

If you are keeping a betta fish in a vase and cannot filter it, then you will have to change the water much more regularly to prevent ammonia, nitrite, and nitrate build up. Also, make sure you are cleaning the tank or vase regularly to stop algae from forming.

Do Betta Fish Need Heaters?

Yes. Remember, betta fish are native to places with hot, humid weather and monsoon seasons. Even though koi betta fish are created through selective breeding, the need for warm water has not been bred out of them. In places like Thailand, the water is always warm. Therefore, you should supply your betta fish with a submersible heater.

Be aware that exposing any fish to water above their tolerance level is also dangerous. You should never keep your koi betta fish in water hotter than 85 degrees Fahrenheit, and even that will be dangerous for too long. Hot water temperatures will accelerate their metabolism and cause the fish to age rapidly.

Conversely, if the temperature is too cold, your betta fish will be sluggish and its immune system will be compromised. That can increase the risk of infections that will shorten its lifespan.

If you have a tank smaller than 5 gallons, however, you do not need a heater.

Do Betta Fish Need Lighting?

All living things require a little bit of sunlight—unless it’s dredged up from the abyss! Even though betta fish are usually dwelling in places with thick vegetation, they do enjoy lighting. They also enjoy a daily schedule of day and night.

If you provide them with light, make sure you have aquarium LED lights with timers, so the lights shut off automatically. Optionally, you can get lights with day and night settings if you have the tank somewhere that doesn’t get a lot of natural light.

Setting Up a Tank For Your Koi Betta Fish

Now, let’s look at some steps to setting up a successful tank for your koi betta fish:

  1. Purchase the tank – The minimum is 2.5 gallons, but you can go much bigger. 5 gallons is the recommended size for just a betta. If you want tank mates, choose at least 10 gallons.
  2. Choose the ideal location – Never place a tank right beside a window, since that puts the fish at risk of overheating. Also, avoid too much ventilation, such as HVAC outlets and radiators. Choose a flat, stable surface for the tank.
  3. Add some substrate – Gravel is the best choice for betta fish.
  4. Add water – Once the substrate is in place, add some water to the tank.
  5. Install the heater and filter – Switch both of this on and start working to get the water to the right conditions.
  6. Add the decorations and plants – Next, add the live and/or artificial plants and any other decorations, like plastic caves and hiding spots, to the aquarium.
  7. Do a water test – Make sure you test the water parameters before moving onto the last step.
  8. Introduce your betta to the tank – Introduce your betta fish to the tank (and the tank mates) then give them some food. Though your fish might not eat right away in the new tank, they will soon get comfortable and will enjoy their snack.

Compatible Tank Mates For Koi Betta

Thinking about pairing your koi betta up with some brightly colored tank mates? Luckily, there are a number of fish that you can add to a tank that your betta fish will not fight. Just remember that two koi betta males is a terrible idea.

If you want to have an aquarium with more than a betta fish, then you need to choose tank mates with the following traits:

  • Tropical (warm water) fish
  • Short fins
  • Dull color
  • Peaceful

The reason behind these traits is based on the betta’s tendency to attack anything that even looks like a threat. If you have a fish with long fins and bright colors, your koi betta might assume the other fish is a danger. That is why you need fish with duller colors and placid personalities.

Here are some of the best tank mates for koi betta fish:

Corydoras Catfish

Corydoras Catfish

Corydoras, also called cories, are timid fish that often live in schools. You can keep 5 in a 10 gallon tank without any problems. Since they are bottom-feeders, you rarely have to worry about them coming in contact with the betta fish and causing a scene.

Kuhli Loach

Kuhli Loach

Loaches are peaceful, bottom-dwelling fish that will scavenge for food along the substrate. Again, this will keep them away from the betta. Just make sure that you are using sand as substrate instead of gravel.

Unlike other kinds of guppies, feeder guppies are bred to serve as food for larger fish and don’t have very bright coloring or long fins. This makes them great companions for betta fish. Also, guppies are fine with living alone, so you can add one or two and not have to worry about schooling behaviors.

You can also consider neon tetras and ember tetras. Even though these fish are brightly colored, they are small, quick swimmers. Tetras can dart around the tank, far from the betta, thus preventing any battles from ensuing.

What About Marimo Moss Balls For My Betta’s Tank?

Marimo balls

You should definitely consider moss balls for your fish tank. The marimo moss ball is an amazing plant that does wonderful in 5 gallons or more. Betta fish love these moss balls and are often seen playing with them. The best part is that moss balls do not grow uncontrollably; they only grow about 5 millimeters a year. Plus, they can live for 100 years, even in poorer conditions; so if you don’t have a green thumb, no worries.

The best part? A marimo moss ball or two will help keep the water conditions perfect for your koi betta fish. They are both algae and nitrate eaters. They also produce additional oxygen. If you don’t know how many moss balls you need for your fish tank, we answered that question already. Click here to find out more!

Common Koi Betta Fish Behaviors To Know

Lastly, we are going to touch on some common betta fish behavior. Knowing when your fish is excited or stressed can help you figure out if they are healthy or not.


When you see your brightly colored koi betta flaring its gills and fins, you might be concerned. Don’t worry too much. Flaring is meant to be intimidating, so the betta might do this around a tank mate, another male, or even its reflection. Moderate flaring is perfectly fine, but if you fish is doing this for more than 20 minutes a week, you might want to consider changing the environment to remove stressors.

Bubble Nest Building

Given the correct conditions, you might notice your male koi betta build nests made out of bubbles. This is instinctual. Males build nests to show that they are ready to mate.

Jumping From The Tank

Many betta fish are known to jump from their tanks. This is another act of instinct. During drier seasons, fish will jump from one puddle to the next—or at least hope to move into another body of water.

Jumping can mean other things, however. The tank may be too small, thus prompting your fish to look for another, larger space. The water may be too cold or toxic. Sometimes, hungry betta will also jump from the water.

Surfing Glass

Usually, when betta hug the glass wall of the aquarium or vase, it means that they are stressed or preparing to jump out of the tank. That said, if your fish immediately heads to the glass when you approach, it could mean that it is hungry and is expecting some food or another interaction.

Final Thoughts on Koi Bettas

Koi betta fish are stunning fish with bright koi-like patterns and fins. Aside from these unique color variations, koi bettas are very much like other types of betta fish, and you should care for them accordingly. Make sure the tank set up is going to support your betta, so you can enjoy their brilliant fins and personalities for as long as possible.

You are viewing this post: Koi Betta Fish: Complete Guide. Information curated and compiled by Congofishes.net along with other related topics.

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