How Fast Do Betta Fish Grow?

Are you planning to breed your bettas for the first time and are wondering how long it’ll take your fry to grow? Did you buy a baby betta from the store or a breeder and want to know when your fish will grow to full size?

If you answered yes, then you’re probably wondering, how fast do betta fish grow?

Betta fish are somewhat slow growers compared to their life span. Still, this can make things fun for you if you enjoy watching your fish grow.

How Fast Do Betta Fish Grow?

Betta fish grow fastest when they are in their juvenile stage. They will grow a few millimeters every week and will begin to mature at just 9 weeks of age.

Yet, most bettas don’t reach their full size until about 7 months of age. Betta fish generally live for about 2-4 years, so it might seem odd that it takes them that long to grow to their full size. Still, there doesn’t seem to be any reason for this.

A Betta Fish’s Juvenile Stages

When a betta fish hatches from its egg, it will only be about 0.1 inches (2.55 mm) long. The fry is so small at this point that you won’t even be able to see their tail.

For the next several weeks, the fry will grow about 0.05-0.1 inches (1.3-2.54 mm) every week. Around week 5, their growth will begin to speed up a bit. They will begin to grow about 0.1-0.25 inches (2.54-6.35 mm) every week.

At 9 weeks of age, your betta fry will continue to grow at about the same rate. Yet, this is the age when the bettas really begin to start maturing. Their true colors will begin to come in, and they will start to become aggressive.

It is at this age that you’re going to need to separate the males from each other. You will likely need to separate any large females from the smaller females as well.

Most breeders keep their betta fry in small containers until they find a home. Still, others provide separate tanks for each fish. Choosing the best betta fish tank size is also an important consideration

Your betta’s growth will really begin to slow down around 11 weeks of age. You may not see much noticeable growth, but your betta will continue to grow until about 7 months of age.

Check out this list for a more comprehensive breakdown of betta growth, to give you an idea of how big do betta fish get:

What Influences A Betta’s Growth?

The main thing that influences your betta fry’s growth is the water quality. Baby bettas are very fragile and susceptible to poor water quality. It is imperative that you closely watch your water parameters to ensure they are safe for your fry.

Another factor that influences your betta fry’s growth is the food you provide. Nutrition is very important for growing fish. If you don’t provide the right food, your fish’s growth may become stunted.

Newborn bettas are going to eat different food than those who are a week old. Those who are a week old will eat different foods than those a few weeks old.


It will take your betta fish about 7 months to grow to full size. Yet, bettas begin to reach maturity around 9 weeks of age, and this is when their color and aggression set in.

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