How to Tell the Age of a Betta Fish

How to Tell the Age of a Betta Fish?

How to Tell the Age of a Betta Fish

When you adopt a cat or dog, they normally come with papers proving when they were born. If not, most vets will be able to estimate their age down to a few months. However, when you simply look at a fish, it is difficult to determine how old they are. This is especially an issue for betta fish, given their small size, and the fact that most people do not know how long they live.

In order to determine the age of a betta fish, you will need to identify a few physical characteristics. It is often easier to determine age of a male betta fish, as their coloration is more prominent, and you can partly tell their age based off of coloration. Luckily, there are several other factors that you can use to determine the age of your betta fish.

In this article, we will discuss the size, back, lethargy, eyes, scales, and fins, stripes.


As with all living things, bettas grow as they get older. Sometimes you can determine the age of juvenile betta based on their size. When they first hatch, they will be so small that you will hardly be able to see them. At the age of two weeks, they are roughly a quarter of an inch in size.

The smallest baby that you would be able to buy would be a bit over half an inch in length. These fish are normally only five weeks old. This is the average age and size during which they begin to take prepared food, meaning you can buy them at this stage.

Bettas continue to grow only for three or four months, reaching an average size of about two inches long, though males are typically larger than females. After this four-month period, it is difficult to determine the age of betta based on size alone, so you must use some of the other options.

In addition, it helps to know whether your betta is male or female. While females are considered full-grown at or around 2 inches, males can reach up to a full inch longer than the females. Though, again, while this will only help for the first three to fourth months of life, it can still help determine the age of young betta.


One primary sign of older betta (most ages over 1 year) is a humped back. Older bettas tend to develop a raised back, similar to that of older humans. This occurs in both male and female bettas and is generally a good sign that your betta is older in age.

That being said, this does not mean that your betta will die soon. The average lifespan of betta is anywhere from 3-5 years of age, and older ages are not impossible. However, you may need to change a few things about your betta’s tank once they hit this age.

It is a good idea to add more resting areas to the tank, both at the mid-level and upper level. As betta ages, it becomes more difficult for them to move around. That being said, they still need to be able to easily access the surface of the water to breathe air.

By adding more resting areas closer to the surface of the water, you’re making life much easier for your betta. This helps reduce stress and prevents them from straining themselves by moving too often and too much. In addition, be extra cautious about sharp objects in the tank, as they may have less maneuverability.


As previously discussed, it becomes more difficult for a betta to move around as they age. They will act more lethargic, rest more often than before, and will generally be less active. The same thing happens to people when they age as well.

This is a normal part of growing old and can be expected in most pet species. However, if you have other signs that your betta is very young, such as them still being a small size, lethargy will not be related to old age.

Instead, it is very likely that your pet is sick. Lethargy should not start to show until around a year and half of age (though a few months before this is not worrisome), so if your betta becomes lethargic early in life, you should monitor them closely for other signs of illness.

Most illnesses that bettas can contract will come with obvious symptoms. For example, cloudy eyes, a gold sheen, a caved-in the stomach, torn fins, blackened fins, a red belly, and many other signs each point to specific illnesses. You can find more information on betta illnesses in some of our other articles.


If you ever look closely at a betta’s eyes, you will notice that they are incredibly delicate and detailed; similar to our eyes. In fact, bettas are even capable of seeing every color that we see. As they age, they are more prone to developing eye infections, or eye complications.

Cataracts are not unheard of in bettas, but a cloudy eye is most likely a type of eye infection. These can normally be treated with extra water changes, or, if necessary, antibiotics. However, old bettas may naturally develop cloudy eyes, purely due to age.

If this begins to impact their sight, you will need to take precautions to protect them. If they have tankmates, watch them closely to ensure that the other fish are not picking on them. In addition, ensure that they are able to get enough food. If they are, they will be able to live out the rest of their life happily.

Scales and Fins

The scales and fins of older betta will look very different from that of younger betta. Very young bettas, such as those under two months, normally have translucent fins without many colorations. The fins will also be very small.

As they grow and age, their fins will begin to develop striking coloration. However, after reaching over a year in age, you may notice that the coloration in the fins seems to fade. In addition, the scales normally take on a duller appearance as well.

However, if your betta is still relatively young (younger than a year) and you notice a dramatic decrease in their coloration, one of two things is happening. The first is that they are either stressed or ill, or both. Take the proper steps to ensure that they are not stressed and keep your eye out for any signs of illness.

The other possibility is the marble gene; this gene is randomly activated throughout a betta’s life and causes them to permanently change colors… at least until the gene activates again. Bettas normally revert to darker and darker colors as time goes on, changing from bright reds and oranges to deeper blues, purples, and blacks.

These color changes should not be a concern, but if you are noticing black scales and black on the fins, you may want to consider ammonia poisoning as a possible factor. This type of poisoning leaves black chemical burns on fish and is often lethal, so it is best to catch this type of poisoning as soon as possible.


One can often see stripes on very young bettas under two months of age, simply due to the fact that they have not fully grown their color. These stripes are horizontal along with their bodies and are used to blend into their surroundings in the wild, similar to spots on a baby deer.

While bettas are able to make these spots appear throughout their whole lives, it is not a good sign if you see these stripes on an adult or older betta. These stripes are then called “stress stripes” and only appear if betta is extremely stressed.

On the other hand, if you are seeing vertical stripes appearing on your betta, these are breeding stripes. While they can also signify stress, they normally only appear when betta wishes to mate and is around other bettas, so the average keeper does not often see them.

In conclusion, while it is difficult to determine the exact age of betta unless they are a baby, you can determine the general age of a betta through a variety of factors. If they have a hunched back, are over 2 inches in length, and have dull colors, they are over a year and a half old. If they have transparent fins and are only a quarter of an inch long, they are 2 weeks old. By using a variety of these factors, you will be able to tell how old your betta is and take care of them accordingly.

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