Do Betta Fish Grow (How big & how fast do they grow)


Bettas fish, also known as Betta Splendens, or Siamese fighting fish, are a popular choice for home aquariums. They are known for their vibrant colors and elegant fins, but how big do betta fish grow, how big do they grow, and how fast do they grow?

On average, a healthy betta fish can grow to a maximum size of around 3 inches or 7 cm in length when fully grown. Bettas typically reach full size within 6-12 months. However, this can vary depending on their care, tank size, and your betta fish’s genetics.

Do Betta Fish Grow

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Several factors can affect how big and how fast your betta fish will grow, which I will cover in this short article. If you have any questions about a bettas growth rate or how to make your betta fish grow bigger, keep reading and you will find the answer.

Betta Fish Growth Chart

As this article answers the question “do betta fish grow?” it would be a good idea to start by discussing a betta fish’s growth stages. Below is a betta fish growth chart with average sizes at each stage of its life.

Betta AgeApproximate Size
Birth 0.03 inch (0.08cm)
1-2 weeks old0.2 inch – 0.25 inch (0.5cm – 0.64cm)
3-5 weeks old0.35 inch – 0.6 inch (0.89cm – 1.52cm)
6-8 weeks old0.85 inch -1.3 inch (2.16cm – 3.3cm)
9-12 weeks old1.55 inch – 2.1 inch (3.94cm – 5.33cm)
12-24 weeks old2-2.5 inches (5.08cm – 6.35cm)
24-48 weeks old2.5-3.5 inches (6.35cm – 8.89cm)
Approximate size of a betta fish throughout its main growth stages

Although the sizes above are typical, some factors can cause a betta fish to grow bigger or smaller, which include:

  • The quality of care your betta receives.
  • The size of your betta tank.
  • The genetics of your betta fish.
  • Your betta’s diet.
  • The general health of your betta fish.
  • Water Quality
  • Water Temperature

We will look at some of these factors later in this article.

Betta Fish Growth Stages

The betta fish’s growth stages occur from birth (as fry) until fully developed. There are several stages to a bettas growth cycle which you will find in the table below.

Betta AgeMain Growth Characteristics
Birth to 1 week oldThey Will stay near the top of the tank, are very transparent, and lack fins.
1-2 weeksTail growth and dorsal fin beginning to form.
3-5 weeksGrowth spurt, the body has almost doubled in size and some coloring is showing.
6-8 weeksColor is more defined and further fin growth.
9-12 weeks– Female fins are usually fully grown.
– Male fins continue to grow.
– Become sexually active.
Males should be removed from the tank and placed in separate tanks before aggression shows.
13-16 weeksColor continues to develop in some males with further fin growth.
17-20 weeksMales should be close to fully developed fins depending on the variety. Longer finned betta can take 6-10 months for full development.
Main characteristics that betta develop throughout their growth stage

Throughout your betta’s growth stages, you should give them a high-quality diet and monitor their health closely to provide them with the best chance of survival and a healthy lifespan.

How Fast Do Betta Fish Grow

Baby bettas generally grow quickly, but their growth rate will slow down as they reach adulthood. Most fully grown betta fish are around 6 months old, but male bettas can take up to 12 months to fully develop their fins. Some factors can affect a betta fish’s growth rate, such as the quality of their diet and water conditions.

As I mentioned above, there is a slight difference in how fast male betta fish grow compared to female bettas. Male betta fish have much larger fins and plumage which make up a large portion of their size and will take much longer to grow to full size.

How Big Do Bettas Get

You can see from the charts above that most of a betta’s growth will occur during the early stages of life, so how big do bettas get when fully grown, and what are the main factors that will impact their growth?

The sizes I am discussing throughout this article relate to average betta fish, but a reasonably new variety has been bred: King bettas. King betta fish are slightly larger and usually measure around 3 – 4 inches when fully grown. King bettas also have much thicker bodies and larger fins.

How Big Do Male Betta Fish Get

Male betta fish typically reach an average length of 2.5 – 3.5 inches when fully grown, with the majority falling in the middle of this range. The record size for a male betta fish is 4 inches, but this is quite rare.

A large amount of male bettas size is made up of their fins, which can grow to be around 1/3 of their total length. So, if you see a betta with very long fins, he is likely a fully grown adult.

How Big Do Female Betta Fish Get

Female betta fish typically reach a length of 2 – 3 inches when fully grown, with the vast majority falling in the middle of this range.

The main difference between male and female bettas is that females have much smaller fins than males. Female bettas tend to reach full size much earlier, although both males and females become sexually mature at around 6 months of age.

How Big Do Betta Fish Get In The Wild

Betta fish growth rate and size do not differ in the wild compared to bettas in captivity. The main difference is that wild bettas tend to have shorter fins and less unusual coloration due to the lack of selective breeding in the wild.

The typical size for a wild betta fish is 2 – 3 inches, with males on the larger end of this range and females on the smaller end. There is also less chance of wild betta suffering from stunted growth, which can be caused by a tank that is too small. A bettas natural habitat also provides the best food sources.

How Big Do Bettas Get
Betta fish growth in the wild is the same as in captivity.

The main difference between betta fish living in their natural habitat is their lifespan. A wild betta fish lifespan is often significantly shorter than those in captivity because of regular aggressive confrontations with other betta fish. In captivity, it is advised to keep male betta fish in separate tanks.

Bettas that live In community tanks are usually mixed with smaller, less aggressive fish species.

How to Make Your Betta Fish Grow Bigger

If your betta fish doesn’t seem to be growing very much, it could be genetic, which you cannot change, or maybe there is a problem with the water conditions or diet.

Let’s look at how you can make your betta fish grow bigger.

Diet

One of the most common reasons for a betta not to grow properly is because they are not getting enough food. In the wild, bettas would eat small insects and larvae, but in captivity, they are usually fed pellets or flakes, which don’t contain as much nutrition.

It’s important to give your betta a varied diet to ensure they get all the nutrients they need for proper growth. You can read our article: Why Won’t My Betta Fish Eat? – 6 Possible Reasons Why for more information on this.

So what do betta fish eat:

  • Bloodworms
  • Blackworms
  • Mosquito larvae (no more than one per week)
  • Frozen brine shrimp and daphnia
  • Cut up pieces of earthworm or nightcrawler

All food types above can be given as live food, or you can buy frozen or freeze-dried for convenience. Live food has the highest nutritional value, however, good quality frozen food is also quite nutritious. If you opt for freeze-dried food, it has the lowest nutritional value, but its treatment makes it less likely to carry harmful parasites or diseases.

Betta fish are omnivores, but protein makes up a large part of their diet and will profoundly impact their growth rate. Vegetation is necessary to aid a bettas digestion which will help reduce the chances of betta constipation.

Softened or blanched peas are a great source of vegetation and are also suitable for easing digestive issues, or you can provide lettuce leaves and small portions of shredded, soft fruits.

A good quality betta fish food can provide many of the nutrients necessary, but for the best growth, you should always supplement a bettas diet with live or frozen foods (especially when they are young).

Betta growth from 0-5 months

Water Quality

Another common reason for stunted growth is poor water quality. If the water in your tank is not clean, it can cause problems with your betta’s digestion and absorption of nutrients, leading to stunted growth.

Poor water quality can often carry less oxygen, affecting your betta fish’s metabolism and causing slow growth. If there are signs that your betta fish tank is low in dissolved oxygen, regular water changes will help, or you can read this article: How Do You Oxygenate A Fish Tank (and why you need to) which will give you some tips to resolve the problem.

Juvenile bettas are also known to release a growth-inhibiting hormone (GIH) intended to limit other betta fish’s growth potential, giving them a better chance of being the larger, dominant fish. If a tank is too small, a betta will be exposed to the GIH, limiting its own growth potential. Regular water changes will remove most growth-inhibiting hormones from the water.

It’s important to test the water in your tank regularly and make sure the parameters remain within the safe range for bettas. You can read our article on betta fishOpens in a new tab. care to find the correct water parameters.

I also have several other useful articles on betta water which you can find below.

How often to change betta water.

How often do you clean a betta fish tank.

What water to use for betta fish.

Water Temperature

The water temperature in your betta tank can also impact your bettas growth. Water that is too cold can slow a betta’s metabolism and make it harder for them to digest their food correctly, both of which can lead to stunted growth.

For maximum growth, betta fish water temperature should be between 78° to 80° Fahrenheit (25.5° – 26.7° Celsius). If the water in your tank is outside this range, you will need to take steps to raise or lower the temperature as appropriate.

Betta Tank Size

A tank too small for your betta can also impact their growth. Many people wrongly believe that betta fish are happy in small spaces, but this is untrue. So how big should a betta fish tank be? Personally, I wouldn’t recommend a tank smaller than 5 gallons, and if you have the space, 10-15 gallons for a single betta fish is perfect.

A tank that is too small will cause stress to your betta fish, and stress will not only impact a bettas growth, but it can also impact their general health.

If you notice unusual, horizontal stripes developing on your bettas body, these are called stress stripes and are a sure sign of stress. You can read about stress stripes in betta fish in this article: What are Betta Stress Stripes.

I also explained above that betta fish release a growth-inhibiting hormone. If they are in a small tank, they will be exposed to high levels of their own growth-inhibiting hormone, which will likely cause stunted growth.

Wrap Up

As you can see, quite a few factors can impact a bettas growth rate and maximum size. Unlike some larger fish species, the difference between a full-size betta fish and one with restricted or stunted growth is not huge.

Baby betta fry requires good food and a healthy environment for the best growth, and even at the juvenile stage, they will need a protein-rich diet for continued growth. At the adult stage, a betta usually stops growing, so this is the best time to supplement their diets with fish flakes and pellets.

If your betta is a healthy fish, it should grow naturally without any problems. Still, if you notice that your betta fish growth rate appears slower than the typical suggested in this article, you should take note of the factors that could impact its growth. You can often fix potential issues relatively quickly and get your betta growing again.

I hope this article has been helpful.

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Jon O'Connell

I have kept both marine and freshwater fish and set up almost 100 aquariums. Although I am no longer doing it professionally, I am happy to share my knowledge and experience to help others enjoy keeping healthy and happy fish.

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