Do Betta Fish Grow?

Do Betta Fish Grow?

Most fish sold in stores are juveniles and not full grown. For example, the 1-2” goldfish you often see will end up growing to a whopping 8-12”. One of the requirements for living organisms is the ability to grow, so bettas must grow at some point, but will they grow after you buy them?

Small fish cost less than larger fish of the same species, which is why most stores sell juvenile fish. Betta fish mature rather quickly, showing their final color (unless they have the marble gene) after just 3-4 months. Most of a betta’s value comes from its color pattern and fins, so stores try to sell bettas that are mostly mature. These mature bettas will likely still grow once you buy them, sometimes significantly.

In order to fully assess how much your betta will grow, we will discuss the impact of its environment, food, water changes, the “baby” bettas, “king” bettas, and their adult age and size.


One widely circulated myth is fish grow to fit the size of their container. This is woefully incorrect, but it is easy to see where they may have come from. When fish live in a container that is too small for them, their external body stops growing and they become stunted. However, being small isn’t the main problem. The problem that arises is the internal organs continue to grow, run out of the room, and crush themselves.

When bettas are sold in stores, they are often kept in tiny little cups. If left in the cups for more than a few weeks, they run the possibility of becoming stunted. However, you could reverse this if you keep them in a large enough tank.

In order for a betta to reach its maximum size, a 5- or 5.5-gallon aquarium is required. This aquarium gives the fish enough room to swim around and grow fully. The tank also needs to have a filter and heater in order to keep your fish healthy.

Most importantly, keep your fish healthy. Healthy fish are much more likely to reach their full size. Therefore, the heater should keep the aquarium between 78- and 82-degrees Fahrenheit. This is the optimal temperature for bettas and keeps their metabolism exactly where it should be. Since the temperature regulates your fish’s metabolism, heaters are necessary to keep your fish’s metabolism stable. A stable metabolism is essential to the overall health of your fish.

The filter is necessary to keep the water cycled and clear. The nitrogen cycle is essential to keeping betta fish, so please read up on that before buying your fish. If there is no filter and the tank is not cycled, so the fish will be burned by nitrogen compounds, and the burns can limit your fish’s growth.


Just like a little kid, your betta will not grow without the proper nutrition. When it comes to fish, they need a more balanced diet than just pellets. Pellets are still essential, as they provide vitamins and nutrients that are not in all food.

Betta fish are carnivores, so they need a lot of protein to grow to their full potential. In the wild, betta fish primarily eat small crustaceans and insects, some of which will be available at your local pet store. The most common bugs you will find for your betta are freeze dried bloodworms.

These “worms” are actually midge fly larvae. Bloodworms are high in both protein and fat, which can cause an issue. Bettas cannot digest large amounts of fat, so they can only eat bloodworms sparingly. However, this does not mean they can’t be fed bloodworms at all, just in moderation. The general recommendation is to feed bloodworms only one to two times a week, and only one to three worms at a time.

Frozen bloodworms are much better for your betta than freeze-dried ones. When food is freeze-dried, it loses a great deal of nutritional value, unlike freezing the food. Frozen food is much better for your betta as it will help them grow and display their best colors.

Some other fantastic frozen foods are daphnia, Mysis shrimp, and brine shrimp. These are all small crustaceans, like what bettas would find in their natural habitat. Daphnia can also cure bloat in bettas. Mysis and brine shrimp are full of great vitamins and protein and are some of the best foods for your betta. However, brine shrimp do have a relatively high salt content, so overfeeding can lead to swim bladder problems.

Water Changes

Food and environmental factors may seem like the most important factors in growing your betta, but this is not the case. Water changes get rid of excess nitrogen compounds in the water. Nitrates are the final stage of the nitrogen cycle and are safe when under 20ppm.

However, nitrates are extremely rare in natural bodies of water and are often 0 ppm. Additionally, nitrates can negatively impact food fish, even in amounts under 20ppm, so it is possible that even very low nitrates can harm your fish. Keeping nitrates as low as possible is the best way to keep your betta growing.

Aside from keeping nitrates low, water changes also help remove growth inhibiting hormones (GIH) from the water. Juvenile bettas produce hormones to limit the growth of other bettas, but when kept in small aquariums, they will stunt themselves. In the wild, this gives them a better chance of outcompeting the others, but in captivity, it just results in small bettas.

While your betta is still young, you will want to carry out more than just weekly water changes. Doing a water change two or three times a week will remove the hormones from the water and increase your betta’s size. I have seen extremely small betta, with a body less than 1”, because its owner only did water changes once a month while it was young.

Baby Bettas

If you go to certain stores such as Petco, you may find a section of betta cups that contain incredibly small bettas. The store labels these as “baby bettas”, and they are often only 4-7 weeks old. These bettas tend to be only a half inch in size, with many under this size.

Most chain stores do perform some water changes on the cups, but they are never enough. The cups normally test between 2-8 ppm ammonia, which is extremely harmful. The ammonia can burn the gills and reduce the amount of oxygen the fish gets. As a result, the lack of oxygen can limit their growth.

The cups also have large amounts of the growth inhibiting hormone. If they are surrounded by GIH for weeks, it is unlikely that the baby bettas will reach their full potential.

If you get the babies within a week or two of them arriving at the store, they will still have the potential to grow rather large. When caring for these small bettas, it is very similar to an adult. You will want to carry out more water changes, try for once every two to three days, and you will have to feed smaller food. Other than that, their care is the same as the adults.

“King” Betta

Another recent addition to chain stores is the “King betta”. These bettas are much larger than the others you will see in stores and often look much sadder in their cups. The common pet store betta is Betta splendens. The king betta’s origin is unknown, but it is either a domesticated form of a different betta species or a hybridization between splendens and another.

Their lifespans are shorter than their colorful counterparts as they often only live for two or three years. Betta splendens, on the other hand, normally live for 4-7 years, though damage from cups can cut their lifespans.

The king bettas need the same care as other pet store bettas, but they can reach much larger sizes. The body size of males is often 3”, though there are some reports of these bettas reaching almost 4”. They do require a larger tank because of their larger body size, so a 10 gallon is perfect for them.

Adult Age and Size

For the average betta, their adult size is between 2” and 2.5”. Since most bettas in pet stores are between 1-1.5”, your betta definitely has the potential to grow! Keeping them in tip top shape will leave you with impressive betta, both in size and coloration.

In terms of age, most bettas are around 4 and 5 months of age in pet stores. However, you may find some that are much older if they have been sitting in the stores for a while. Bettas are adults after they are 7 or 8 months old. After this age, there is not much chance of them growing, unless stunted. If they are stunted by their container, they can still achieve a larger size after they live in an appropriately sized one for a few months.

In order to help your betta grow to its full potential, you must provide it with the proper resources. Many water changes, properly filtered and heated water, and quality foods are the best tools to use. These will keep your betta healthy, happy, and displaying its best colors. Keeping your betta healthy will help it grow and leave you with impressively sized betta.

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