Koi Betta: Betta splendens Marble Variation

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. Their aquarium husbandry does not differ from that of any other betta fish variation, but their beautiful colorings can lead to some unfortunate health problems.

Keep reading to find out everything you need to know about koi betta fish and keeping this variation in your own freshwater aquarium!

About koi bettas

Koi bettas are a specific variation of marble bettas. 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!

Because these fish have been selectively bred, you will not see a koi betta fish variant in the wild. However, Betta splendens do naturally live in and originate from stagnant rice paddies and swamps in Southeast Asia, which you can read more about here.

There are a few different types of marble bettas, including nemo, galaxy, fancy, and of course, koi. Regardless of their coloration, they are still Betta splendens and require the same care as any other betta.


With a fish that changes colors, how can you correctly identify it? Luckily, it is easier than it seems.

Koi bettas are named after their unmistakable patterns of reds, oranges, and blacks, against an iridescent white body that closely resembles the markings of a koi fish (?Cyprinidae family). They are usually a short-tailed variation, similar to the finnage seen on plakat betta fish.

Male betta fish will have more intense colorations and slightly more ornate fins than females.

How big does a koi betta get?

Like other Betta splendens, the koi betta only grows to be about 3 inches long (7.6 cm). For this specific variation, allowing additional headspace for finnage is not too important.

Koi betta behavior

Just because these fish resemble koi fish in color does not mean that they have the same demeanor! The koi betta is still a Betta splendens and carries all the traits and personalities of other betta fish.

Despite their aggressive, betta fish have amazing personalities that make them worth keeping on their own. Betta fish are some of the most interactive fish to have and many hobbyists have even claimed to form relationships with their fish.

Koi Betta

Are koi betta aggressive?

Yes, koi bettas are aggressive just like any other betta. They become extremely territorial towards other male betta fish and will fight until the death. It is not unheard of for a male betta to display aggression even towards his own reflection on the side of the aquarium!

Never place two male betta fish in the same tank.

Koi betta tank requirements

Koi betta fish will need to be kept alone in smaller tanks due to their aggression and to really let their color shine. Betta fish will need at least a 5 gallon (18.9 L) heated tank to themselves. Water quality will need to be maintained through regular aquarium maintenance and adequate filtration.

Betta fish may be kept on gravel or sand. It is also encouraged to give your betta plenty of live plants to recreate their natural environment and create hiding places throughout the tank. Other hiding places can also be made out of smooth rocks and driftwood.

If wanting to keep your betta with other species of fish, a minimum tank size of 15 gallons (56.8 L) is recommended. Remember, each betta fish has a different personality and there is a chance that your betta will not accept new tank mates.

Water temperature will need to be consistent between 77-83° F (25-28° C) with pH between 6.5-7.5.

Koi betta diet

In order to maintain their intense colorations and overall health, betta fish need a high-quality diet. Betta fish are omnivores in the wild, but mainly require a carnivorous diet in an aquarium setting. Flakes and pellets that are high in protein and low in fillers should be offered to your betta daily. Live and frozen foods, such as brine shrimp and bloodworms, should be given a couple of times a week.

Betta fish can be picky eaters, but they can also have quite the appetite once you discover their preferred palette! Betta fish are especially susceptible to becoming overweight and constipated, so make sure to not overfeed and break up any pieces of food that might be too big.

For more information about betta foods and scheduling feedings, make sure to check out our full betta food & feeding guide here.


Unfortunately, because betta fish have been manipulated and bred so many times to achieve perfect results, these fish have instead become more susceptible to disease and morphological problems. Some of the most common problems to arise are fin rot and swim bladder disease, but luckily, those are usually easily fixed with medication.

One of the more devastating consequences is possible tumor growth. Tumors will usually look like an abnormal growth on some part of the fish, however, some tumors can also be internal and cannot be seen. The good news is that not all lumps are necessarily tumors!

Once an abnormality has been spotted, remove the fish from the tank and place it into a quarantine/hospital tank. This lump may be the result of superficial abrasions, bacterial infections, or ulcers. It is best to examine the fish and treat the problems respectively. Unfortunately, if it does prove to be a tumor, there is little hope other than surgical extrication; the betta will sadly need to be humanely euthanized in most situations.

Koi Betta Fish


With so many different Betta splendens to choose from, the koi betta may have slipped past you in your searches for a beautiful fish. Because their fins have not been excessively bred, they’re just as easy to keep as most other variations. Their changing colors also make them a true wonder to watch in the aquarium!

If you have any questions about keeping koi betta or need more information about betta fish in general, don’t hesitate to leave a comment below!

Also, make sure to check out our ultimate guide to betta fishkeeping here!


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