Why Is My Betta Fish Flaring its Gills?

Why Is My Betta Fish Flaring its Gills?

There are hundreds of thousands of fish species kept in aquariums and each species has its own unique behavioral patterns. Bettas, for example, often expand their gill plates outwards when they feel threatened. This is referred to as flaring and can be an impressive display of finnage and color. The bettas thrust out their gills and straighten all their fins to look as large and impressive as possible.

There are several reasons for a betta to begin flaring. If they feel someone or something has entered their territory, they will flare in order to chase it off. This is by far the most common reason for your betta to flare. However, there are a few other reasons, which we will discuss.

In this article, we will cover intimidation, flaring at tank mates, reflection, stress, breeding and excitement.


When betta sees a new fish enter their territory, their first reaction is to flare their fins and gills. This is meant to tell the other fish, “This is MY territory!”. Betta fish are small fish, but by fully extending their fins and gills, they make themselves look larger.

In fact, their whole display of trying to make themselves look bigger is to intimidate the other fish. Obviously, this won’t work on larger fish, but for other smaller fish, it normally does the trick. For example, the flaring has the largest impact on other bettas, but some species don’t get the message.

In the wild, bettas do not have long fins and are not as aggressive. They tend to hide when confronted with other fish, even if it is another betta. However, when breeders created the domesticated, long finned betta, they focused on the fins and aggression.

In captivity, bettas cannot hide or swim away due to their long fins. Because of this, they turned back to intimidation by flaring in an attempt to scare away competition or threats. This is why betta fish always fight. Their behavior is vastly different from that of wild betta, and it has its own unique quirks.

Tank Mates

This aggressive nature of bettas makes it difficult to keep them with tank mates. Even if you end up with extremely docile betta, it will flare at tank mates at some point. On the other hand, if you end up with an aggressive one, it will attack and bite its tank mates.

The problem with flaring at the tank mates is that most won’t understand what it means. For example, when a human blinks slowly, it normally means they are just tired. However, if a cat blinks slowly, it is signaling that the area is safe.

Just like this difference in physical behavior and its meaning, most fish don’t flare. For instance, if the betta flares at a school of celestial pearl danios, they likely won’t change their behavior at all. They won’t understand what the betta means until the betta starts chasing them.

Since the fish do not understand their warning signs, they can end up injured. Other bettas will understand the warning signs, but they will be more than willing to fight. Some other tank mates are unable to understand the betta charging at them as well. You may be wondering What Kind of Fish Can Live With a Betta Fish without getting hurt?

Shrimp and snails lean towards the skittish side, but once they get used to their surroundings, they will come out into the open. However, the main issue is that they do not have behavioral patterns anywhere near that of fish.

When bettas first get a new tank mate, people often try snails since their shells can protect them. Bettas will often follow the snail around, flaring at it. The closeness of the betta and its attempt to intimidate the snail does not work, since snails do not process forms of intimidation, only attack. For this reason, the snails often get nipped many times before they understand. But two types of snails can live with Betta


However, if you see your betta flaring and you don’t have any tank mates and you see your betta flaring, there is an issue. Most likely, the reason your fish doing this is that it sees its reflection. For instance, betta fish do not pass the self-image test, which means they do not recognize the thing they see in the mirror as “self”. They recognize it as something “other”.

Due to this, your betta will often attempt to attack its reflection. For example, just as you can see a glare on your aquarium from the outside, the light creates a glare on the inside. Depending on how and where you positioned the light, the glare may be intense enough for your fish to see its reflection.

In order to stop this behavior, you will have to change the lighting position or the light. Some bettas will stop attacking their reflection if given enough time, but most will not.

Firstly, you need to determine which side your betta is attacking. If your betta is attacking all sides, you should try adjusting the ambient lighting. On the other hand, if your betta is attacking only one side or two adjacent sides, try moving your aquarium light.

However, if you are unable to find a lighting position or ambient lighting amount that prevents your betta from attacking the sides, you will have to cover the sides of the aquarium. You can add sheets, blankets, or even acrylic paint to the outside of the tank. You will want to leave the front of the tank open so you can view your fish.


The reason that you should fix any problems that cause your betta to flare frequently is because flaring is stressful. They want to remove what they see as a threat from their territory, but most of the time they are unable to. Because they are unable to do anything about the situation, they become extremely stressed.

Some bettas even refuse to eat while the “threat” is in their territory, which, as you can imagine, is an issue. Stress is debilitating to fish and weakens their immune system. Bacteria, fungus, and parasites are constantly in your water. However, your fish’s immune system is strong enough to take care of them most of the time.

By weakening the immune system with stress, pathogens and parasites can work their way to your betta. Your betta will alternate between highly aggressive and lethargic at the very least and will become extremely ill at the worst. At the moment, you need a water conditioner to keep your betta safe.

For instance, some mirror toys are designed to energize your betta. They trick the betta into thinking there is a threat, and he will flare at the mirror. These should not be used for more than five minutes per day, and you should have skip days. If your betta is flaring for more than 20 minutes a week, you need to find a solution.


Breeding is a very stressful time for bettas, but flaring is acceptable here. The male should flare at the female when they are first introduced, but she should display submissive posture soon after. After the male has established dominance, he should not flare.

If the male continues to flare or the female begins to flare, the pair should be separated. This causes severe stress to both participants, which is unacceptable during breeding. The pair needs to be in their top condition, and if overly stressed, they will become ill.


Bettas all have unique personalities, and some bettas flare when they get excited. Some keepers recount stories of their betta flaring at their food every morning, or even at their keeper. Bettas can display flaring without aggressive body posture.

If your betta is one of the rare ones that flares but does not extend fins or show other signs of aggression, it is not a huge problem. You should still take steps to avoid him or her flaring, but most of the time nothing can be done for this behavior.

On the other hand, if you have a betta that flares and displays aggressive behavior towards you and/or its food, this still induces stress. In some cases, you will simply have to limit the time you spend with your pet. However, the good news is that these cases are incredibly rare.

In conclusion, the original betta breeders bred bettas to a standard of aggression and enhanced their natural flaring. Their dependents, the common bettas you see in pet stores, still flare aggressively because of this. If your betta flares excessively, it can cause excess stress and illness, but there are ways to fix this.

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