Are betta fish aggressive?

The domestic Betta splendens is a highly aggressive fish species. Males show signs of aggression to other competing males by flaring their fins and gills and chasing the opponent. Males are aggressive to both other bettas and to other fish species invading territory.

The domestic Betta splendens has been selectively bred for decades. People aimed for the most beautiful, biggest and most aggressive specimens and hybridized the wild Betta splendens to how it looks today.

Are female betta fish aggressive?

Female betta fish are more tolerant towards each other than males are. However, females don’t hesitate to take on each other. Females usually only compete for things like food and personal space. It is possible to keep a group of females together under close supervision. Even females can kill each other and in extreme cases the female.

It is perfectly normal for the females to have small frenzys and conflits to determine hierarchy, but not to harm each other. One female in the group will be dominant and oversee all other females, establishing a clear hierarchy.

Some advice suggests placing a male with a group of females to create a clear hierarchy and that the females will fight less with a male in the tank.

This is not good advice, since a male will do more harm to the females than good. The male will always try to impress the females or chase them away from his territory. This causes the harem to live in permanent stress. In most cases the male will harm the females and if not separated kill them.

Two Betta imbellis females flairing. This was taken in the breeding tank, with the male around. The females where most likely competing for mating. However Betta imbellis is often labeled as a peaceful species, but these females don’t feel like being nice.

Why do betta fish fight?

There are a few reasons why betta fish fight. The most common one is territory. In the wild, Betta fish live in small and shallow pools with lots of vegetation. This vegetation creates small separated pods where males can establish their territory. 

When another male is invading their personal space, a male will see it as an intruder and both will start impressing each other by flaring their gills and fins to look bigger. Showing this aggressive behaviour is a ‘programmed’ thing all betta males have. 

If the intruder/opponent doesn’t leave, things can get very nasty. The initial minutes are just showing off how beautiful both are, but after this males will start physically attacking each other. They will start biting at fins and damaging scaling.

It is not true that betta fish always fight until death. Only in very occasional situations, when males can’t leave each other, it can lead to death of one or both males.

This is why it is impossible to put two betta males together in the same tank. Unless your tank is very, very big both males will be forced to live with each other and thus keep fighting. 

The same applies to keeping betta fish in pairs. However a female doesn’t provide much resistance and will flee away, the male will still try to either impress or scare her away. In most cases the male ends up killing the female, so only put a female with the male for breeding.

Factors that affect aggressive behaviour

Betta males always fight when seeing each other, that’s just their nature. But certain factors do affect how they behave and how aggressive they get.

  • Competition for female

Betta males will show extensive aggressive behaviour when adding/showing a female to the males. This is because of reproduction and obviously both males want to mate with the female, which causes more aggression. In the wild these fights happen regularly too. 

An amateur study found that  males where almost 5 times as aggressive when being shown to a female, in contrast to food or territory. 

  • Protective for offspring

Betta males are extremely protective over their offspring and will not totally tolerate any other fish coming near his nest.  The first days of their life the fry will be fully dependent on their father, who guards them. 

This causes the male to not eat for days and not leave the nest for anything. After the spawn when the eggs have been laid. the male will scare away the female and if not removed from the tank she will be killed.

  • Food

Bettas in the wild can face hard times getting food. if there is a source of food and another betta is there too, males will compete for the food. This is often forgotten when being kept in captivity, since there always is enough food. If you keep a sorority of betta females always provide different food spots, so conflicts are avoided.

Can you keep betta fish together?

Betta fish should never be housed together. A male and a female will fight since they see each other as inrutors. Especially the male will tolerate the female in his territory. 

In the initial days of keeping your pair together, things might go pretty well. It can be that the male isn’t very aggressive at first, but this wouldn’t last long. After a couple of days tensions will run up.

It can just as well be that from moment one male and female are constantly in conflict and both fight. Not separating will result in the female dying and most likely the male wounded.

Only in a tank of more than 30 gallons you might keep a pair successful together, but you have to ask yourself if it’s worth the risk.

Betta species that aren’t aggressive (Peaceful Betta Fish)

Betta macrostoma male flairing
Photo by Sammy Yu

In this article, I only focused on the domestic Betta splendens. But did you know there are 73 species of wild betta fish that are still living in the wild? The domestic Betta splendens is in fact a hybridized version of the wild Betta splendens, that still lives in the wild. 

There are dozens of other wild betta types that all have their own preferred condition, and some can successfully be kept in pairs. Here are three species that under the right conditions could be kept in pairs.

Betta imbellis is often called the peaceful betta for it’s relatively calm behaviour towards each other. However, Betta imbellis still is an aggressive Betta species and males show similar behaviour to Betta splendens towards females. A male will not hesitate to attack a female if she invades his territory.

That being said, in contrast to other wild betta species it is a little more tolerant. Keeping this species in pairs is still at a risk and should be carefully considered. In a tank of at least 20 gallons a pair can be housed. This should be a wide tank with a relatively low water level to allow both to establish their territory.

In most cases a pair will coexist with only fighting occasionally, however there is also a chance that they don’t get along and then they should be separated.

Betta macrostoma or the Brunei Beauty is one of the most appealing wild betta species for most people. Betta macrostoma is a mouthbrooding Betta species that functions well in pairs and once a pair is formed they can peacefully live together.

Betta macrostoma is a big species and can only be housed in a tank of 20 gallons, for one pair. Plenty of hiding spaces and plants should be provided so both can hide if needed. There will always be some small conflicts.

Betta hendra is a small temperamental bubble nesting species. Due to its size, a pair can be housed in a tank of 15 gallons. Again, lots of plants are necessary to provide natural shelter for both. 

Can betta fish live with other fish?

Betta fish aren’t tolerant towards other tank mates. If you decide to put other fish with the betta fish, this should be carefully considered. Some fish species may harm your betta, which causes stress for both.

Keeping tank mates with betta fish can be done, but some preparation is needed. Other territorial species such as gouramis or apistogrammas are definitely a no-go, but small fish can cause problems too.

Your starting point should be your betta fish, which will be the main inhabitant of your tank. Other fish should be compatible with it and in lower numbers to make sure your betta fish has all the space to create its own territory.

To keep a betta male with tank mates a tank of at least 15 gallons is recommended. This tank should at least have some alive plants and shelter in it. So if there would be any conflicts fish can easily hide.

  • Tank mates

There are tons of easy to care for good tank mates for your betta. Depending on the size of your tank, it is best to stick to one or maximum two species apart from your betta. Your betta fish should always be the main inhabitant of your tank and other fish should be chosen so they get along with your betta.