Why do Betta fish fight?

“Why do Betta fish fight?” The answer to this question you will learn and understand through this blog post. Here we will also cover aggressive posture, fight signs and how to avoid when Betta fish begin to fight.

Why do Betta fish fight?

Male Betta fish fight to establish dominance over territory, shelter, or access to females. This aggressive behaviour is common in a diversity of fish species. However, this behaviour may not be innate, Betta fish that are reared in groups were shown to be less aggressive. Fish that are raised in isolation tend to develop more competitive behaviour and fight more frequently.

Conversely, female Betta fish usually do not fight or show any aggressive behaviours. Thus, it is a common practice to keep female Betta fish in small groups. These groups are popularly known as ‘harem’. Inside a “harem”, a hierarchy is normally established, which means that adding a new female may cause an increase in the aggressive behaviour of females fighting to keep hierarchy. 

Historically, male Betta fish were kept as competitive fighters due to their competitiveness and aggressive behaviour. Similar to rooster and dogfighting, this motivation for keeping a Betta fish to fight is an enormous concern for animal welfare.

How to detect a Betta fish fight?

The most common behaviour in a Betta fish preparing to fight is known as “flaring” or “display”. It shows the potential competitors warning signs. Commonly, the gills covers, or operculum, are push and fins are widely spread as an attempt of showing a bigger body size, advising the opponent to leave before the fight.

Once the displaying phase is overcome, a Betta fish fight tends to include a diversity of physical interactions, which may include:

–       Ramming or swimming directly into the other fish;

–       Biting or nipping at the fins;

–       Lock of the lips and wrestle.

If you do not see the Betta fish actively fighting, it does not mean that the fish are not fighting at all. There are few other signs you may see that point to aggressive behaviours, such as:

–       Missing scales;

–       Torn fins;

–       Increased hiding

–       Lethargy;

–       Decreased appetite;

–       Sudden death. 

In case you decide to keep Betta fish together, you must observe the presence of fighting signs. If present, the fish must be separated urgently.

When do Betta fish fight?

Some fighting practices may involve different purposes and behaviours, such as:

–       Dominance/Hierarchy;

–       Feeding;

–       Sexual competition/Breeding.


This is an easy-to-note behaviour. One Betta fish will begin to charge, hit with the head, or even use teeth towards the others. It can result in the aggressed fish being hidden for long periods, or in case of direct conflicts, the Betta fish may stand fighting for hours until the fish give up for exhaustion. This dispute happens mainly for territory, dominance, or hierarchy, and may happen between female Betta fish.


Many competitive behaviours happen due to competition for resources. Normally, feeding resources can cause aggressive behaviours. Thus, aggressive Betta fish may swim around eating all the food and “stealing” from the others. Sometimes they may even hit the other Betta fish until they spit what is inside their mouth. 

Sexual competition/Breeding

Competition between Betta fish males is common to be caused by sexual competition. Access to females for breeding is one of the main causes of Betta fish fights. However, it is also common for males to perform aggressive behaviours towards females after breeding, or even become more territorial to defend their nests.

How to avoid Betta fish fights?

Territory competition

Territory competition is known to be the main cause of Betta fish fights. To reduce the competition for territory and dominance inside a tank, it is important to observe and consider individual behaviour. If your Betta fish gets along with other Betta fish or other species, and do not fight, you could keep them in the same tank. However, it is still recommended to provide hiding spots for the fish and enough space for them. Accordingly, studying and learning about all the species behaviours you consider to have in a tank is highly recommended.

Food competition

To reduce food competition, it is suggested to spread the food throughout the tank and always observe the Betta fish posture. Also, Betta fish are carnivores and require food from different sources. Accordingly, it is possible to offer a variety of natural feeding items in different areas of the water column, using different floating and sinking items. 

Sexual competition

It is suggested to keep only one male Betta fish per tank to avoid access to female competition. In case you may want to reproduce your Betta fish, the recommendation is to keep a small group of females, or “harem”, and a single male. Although, it is necessary that the females do not pose any fighting or disputing for hierarchy behaviours. Thus, it is important to observe and accompany the fish instalment and adaptation.

In general words, the best way to avoid Betta fish fights is to have only one male Betta fish per tank. If you decide to raise fish in individual tanks due to aggressive behaviours, you should provide visual barriers between the tanks, thus the fish would not be able to see each other. 

Mirroring backgrounds or visual toys with mirrors are also problematic for Betta fish, once they can understand their reflections as a competitor. Betta fish might be very sensible when offered these environmental enrichment items. Avoiding reflective surfaces is very important to keep your Betta fish relaxed in the tank.

How many Betta fish can be kept in the same tank?

The answer to this question will depend on the gender you plan to raise. Only a single male should be kept per tank. Females tend to be a bit more tolerant to other Betta fish presence. The tank needs to have plenty of space for them to establish individual territories. If the tank is too tiny or crowded, it is common for females to start to perform territorial behaviours. It is also suggested that males and females should be in the same tank only temporarily, only for breeding purposes.

Betta condo

There is a structure called “Betta condo”, and makes it possible to raise more than one male per tank. These condos are tanks with dividers, walls that allow the water to flow, but avoid animals from seeing each other. There are controversial ideas about Betta fish condos.

Tank size and Territory 

Although keeping multiple males is not advised to be kept in the same tank, it is possible if there is plenty of room for them to establish their territory. Tanks with this purpose should be larger than 20 gallons (75L). In general, the more accurate solution for multiple males is to consider one male per 20-gallon territory.

Current domesticated Betta fish are the result of historical selective breeding. Thus, domesticated Betta fish are more likely aggressive and tend to fish more frequently than wild breed Betta.

Can Betta fish be kept with other species?

Sure! Betta fish can be raised with some fish and non-fish species. Few conditions should be avoided when considering other fish species to a Betta fish tank, they are:

–       Limited tank size;

–       Few hiding spots;

–       Species that resemble a Betta fish;

–       Bright colours;

–       Species with long fins;

–       Species with aggressive behaviours.

Tankmates should be avoided when starting to raise Betta fish. But if you are considering some new mates for you Betta, here are the Betta fish best mates:

–       Corydoras;

–       Black Neon Tetra;

–       Snails;

–       Shrimp.


If your tank has at least 20 gallons (75L), you may be able to raise Corydoras catfish as your Betta mate. A small group of 7 cories would fit perfectly. However, some especially active cories may swim in the middle of the water column, and this could result in a potential fight between the two species, appropriate tank and school of cories should help with the aggression.

Black Neon Tetra

This species is one of the calmest fish species to be kept in tanks. They also are very shy and pacific, opting to avoid conflicts. They do not grow too much, so they will not require too much room in a Betta fish tank.


Snails are a perfect match for Betta fish. They are a perfect match for any fish tank. Snails help to keep the glass and substrate clean. Betta fish tend not to perform aggressive behaviours towards snails unless they are extremely aggressive or hungry.


Shrimp can also be good mates, and cleaners, in a Betta fish tank. However, they are more likely to be eaten by the Betta. Thus, bigger species should not face any issue, and you should not have any problem.


This blog post focused on the question “Why do Betta fish fight?” We understood that Betta fish fight to establish a territory, to show dominance over access to females, shelter, and food resources. The post outlined these reasons why Betta fish fight in detail and scientific behavioural explanation.

Frequently Asked Questions (FAQs): Why do Betta fish fight?

Why do Betta fish kill each other?

Male Betta fish do not necessarily fight to kill the opponent, they try to establish dominance over other males and sometimes over females. However, death is a common consequence caused by Betta fish fights. Open wounds can result in infection and the stress leads to exhaustion, which are normally the causes of death.

Should I let my Betta fish fight?

The answer to this question is “No”. Animal welfare is an enormous concern when considering fish fights. Thus, it is recommended that male Betta fish that show any aggressive behaviour be kept apart from other Betta fish, or even from other fish species to avoid fighting.

Do Betta fish always kill each other?

Betta fish do not fight to aim to kill the opponent. Most Betta fish fights are summarized as nipping and ramming. When the fight results in a death, it is normally associated with infection and/or exhaustion.

Do male betta fish fight with females?

When kept in the same tank, male and female Betta fish may immediately start to fight. Sometimes, they may get along and only start fighting after breeding. Thus it is recommended to keep male and female Betta together only for a short period, for breeding purposes only. It is also possible to keep them in the same tank after breeding, as long as there is plenty of space for them to establish their territory.

How do you know a betta fish is happy?

To determine if a Betta fish is healthy, relaxed, and happy, the following sign should be detected:

–       Vivacious and bright colours;

–       Fins are open, but not pushed or tense – they should move with the water flow;

–       Feeding behaviours readily;

–       Dynamic and suave swimming movements.

Can two Betta fish live in the same tank?

Normally, it is not suggested to keep two males in the same tank, unless they have been reared in groups and do not show any signs of fighting. Betta fish can be very territorial and aggressive, which would result in stress for your fish. However, it is possible to keep a male with a small group of females if the tank has plenty of room for them to establish their own space.

Will a Betta fish kill a Goldfish?

Normally no. A Betta fish tends not to attack a Goldfish and they can normally live together. However, it is important to evaluate the Betta fish behaviour when first meeting other fish, to avoid aggressive behaviours. Although, there are some other reasons these fish should not be kept in the same tank.


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.

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.

Bettas Need More Than Bowls. University of Illinois College of Veterinary Medicine.

Siamese fighting fish. https://en.wikipedia.org/wiki/Siamese_fighting_fish

Chewy Editorial. How to keep your Betta fish Healthy and Happy. https://be.chewy.com/how-to-keep-your-betta-fish-healthy-and-happy/