Two betta fish facing off

Betta fish, also known as Siamese Fighting Fish, are named for their male-against-male aggression. Although individual behavior may vary, most male betta fish in the pet fish trade need to be kept in separate aquariums, and shouldn’t even be able to see other males. Fighting in betta fish can be potentially lethal, so owners need to take effective steps to prevent their male betta fish from fighting.

What Is Fighting in Betta Fish?

The most common fighting behavior in betta fish is known as “flaring.” In this demonstration, a male betta fish will push both operculums (gill covers) forward to suggest a larger body size. This is similar to a puffer fish expanding and flaring its spines when under duress.

Betta demonstrating flaring behavior

Betta demonstrating flaring behavior

Betta demonstrating flaring behavior

calwhiz / Flickr

Other behaviors involve physical interaction between the two fish. Physical interactions may include one fish ramming, or swimming directly into the other fish, or biting or nipping at the fins. Two males may also lock their lips together and wrestle.

Why Do Betta Fish Fight?

Betta fish fight to establish a territory, including food resources, shelter, and access to females. This is a common cause of aggressive behavior in many different fish species.

There is debate over whether this fighting behavior is innate or a consequence of how betta fish are reared. Studies have shown that bettas reared in a group have less aggressive tendencies. It is hard to know with some suppliers how your betta fish were reared and how aggressive they may be, and may take a few weeks for you to be able to tell their level of aggression. Most male bettas, though, are aggressive and cannot be kept with other bettas.

In their native country of Thailand, betta fish have a history of being kept as competitive fighters. Studies observing competitive fights have shown that fish raised in isolation, without other betta fish, tend to be more aggressive and fight for a longer period of time. Just like dog fighting, keeping fish for this specific function is a severe welfare concern.

Female bettas are not usually aggressive to each other. Female bettas are commonly kept in a small group, known as a "harem," and individual fish may be more or less aggressive than others in a group, often leading to an established hierarchy. Once established, the addition of new females to the harem may result in increased fighting as a new hierarchy is established. Female bettas are commonly kept in an aquarium with other fish species of similar size.

While male bettas can’t be housed with other bettas, a single male betta can be kept in the same aquarium with other non-aggressive fish species. Female bettas can also be housed with other fish species. Some betta fish may be aggressive to fish of other species kept in the same tank, if those fish have flowing fins similar to another betta. It is critical to add fish that are not aggressive and good community players to your aquarium. It will depend on your betta’s individual personality to determine if they can be kept with additional species. Some bettas are too aggressive to be kept with any other fish. It is best that betta fish are added to the aquarium last in order to decrease any potential aggressive interactions.

Signs of Fighting in Betta Fish

The most common signs of fighting are gill flaring, ramming or fin nipping. If you do not see your fish actively fighting, you may see other signs, including missing scales, torn fins, or increased hiding. Severe signs include lethargy, decreased appetite, prolonged hiding periods, and sudden death. If trying to keep bettas together and you see signs of fighting, the fish must be separated.

“Fin rot” or fraying fins is a common problem in betta fish, because of their long flowing fins. Often, this is a general sign of illness and a poorly functioning immune system. Another common cause of fin damage is overdecorating with lots of items that can tear betta fins.

How to Stop Fighting

The best way to stop your fish from fighting is to only have one male fish per tank. If keeping bettas in individual tanks, provide a visual barrier between the two tanks so the fish cannot see each other at any time. Simple aquarium backgrounds or a piece of cardboard are effective visual barriers.

Visual toys that have mirrors in them, or mirrors placed near the aquarium should also be removed. Bettas have been known to aggressively respond to their own reflections. Although these may be considered "enrichment" items, these are known stressors in bettas and should not be added to betta tanks. Injuries can occur when betta fish attack toys or their reflections in a mirror.

Treatments have been attempted with marijuana and Prozac to decrease aggressive betta fish behavior. Bettas responded with decreased aggressive behavior with both treatments, but became tolerant of the marijuana dose. Always consult your veterinarian before embarking on any treatments for your pet fish.

Article Sources

The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Iwata E, Masamoto K, Kuga H, Ogino M. Timing of isolation from an enriched environment determines the level of aggressive behavior and sexual maturity in Siamese fighting fish (Betta splendens). BMC Zoology. 2021;6(1):15.

  2. Ichihashi T, Ichikawa Y, Matsushima T. A non-social and isolate rearing condition induces an irreversible shift toward continued fights in the male fighting fish(Betta splendens). jzoo. 2004;21(7):723-729.

  3. González SC, Matsudo VKR, Carlini EA. Effects of marihuana compounds on the fighting behavior of siamese fighting fish(Betta splendens). PHA. 1971;6(3):186-190.

  4. Lynn SE, Egar JM, Walker BG, Sperry TS, Ramenofsky M. Fish on Prozac: a simple, noninvasive physiology laboratory investigating the mechanisms of aggressive behavior in Betta splendens. Advances in Physiology Education. 2007;31(4):358-363.

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