Betta Fish Behavior: Understanding Aggression and Prevention

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?

One of the primary aggressive behaviors in betta fish is 'flaring,' where a male pushes its operculums (gill covers) forward to appear larger, similar to the defensive display in pufferfish.

Physical aggressions include ramming, biting, nipping fins, or lip-locking, where two males grapple with each other.

Why Do Betta Fish Fight?

Betta fish engage in fights mainly to establish territory, secure food resources, shelter, and access to females, common drivers of aggression among various fish species.

Debate exists around whether this aggressive behavior is inherent or influenced by upbringing. Studies indicate that bettas reared in groups tend to be less aggressive. 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 Thailand, betta fish are historically bred for competitive fighting. Studies show that isolation-raised bettas are more aggressive and fight longer. Just like dog fighting, keeping fish for this specific function is a severe welfare concern.

Female bettas are typically less aggressive. They usually form a 'sorority' or 'harem,' where hierarchies naturally develop 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 female bettas together and you see signs of fighting, the aggressive 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.