Discus Fish Size – How Big do Discus Fish Get?

Discus fish can reach about 5-6.5 inches in length (13-17cm) and 6-8 inches in height (17-20cm), so they are quite a tall and large fish. This forces you to get a relatively large tank for them (around 50 gallons per fish), which is quite a lot of space.

However, some discus fish can grow even larger than that. Some fish keepers, according to Wikipedia, have reported their fish have grown to up to 9 inches in height (23cm). That’s quite a large fish, isn’t it?

Their growth and their size is often determined by how you keep them, and what conditions they are given to grow. Also, genetics play a big role in determining how much the fish will grow. Some fish will just be larger by nature, while others may never reach the sizes of larger discus fish.

At about 2.5 years of age, these fish will reach their full size. Up until that age, you’ll need to make sure they get everything they need to reach that size. In this article, we’ll show you what determines the size of the discus fish, and how you can influence their growth to an extent.

Reasons Why Discus Fish Stop Growing

So why do discus fish stop growing? What are the determining factors that influence their size?

1. Aquarium Space

The biggest obstacle discus fish owners face is they don’t provide enough space for discus fish in their tank. Not many of the owners know that these fish are quite large in size, because they don’t seem to be that large once the fish are still young.

But adult discus fish can take up a lot of space in the aquarium. As we’ve discussed, they can reach up to 8 inches in height. This means you will need at least a 50-gallon aquarium for one discus fish, and an even larger one if you want to keep several in the tank.

If the discus fish are limited by the aquarium, their growth will stop. They will not be able to expand their size, and they won’t get enough space to swim around. So they are genetically conditioned to adapt to their environment.

If they become too big for the aquarium, they won’t be able to survive normally. So they will stop growing in order to adapt to the aquarium they are kept in.

2. Water Parameters

Just like human beings can’t live in areas that are too warm or too cold, the same goes for discus fish (and all other fish species, for that matter). You need to make sure the fish get the right water parameters at all times, or your risking to stunt their growth massively.

Discus fish need warm water in order to grow and function properly. If you don’t give them that key environmental need, then they are going to suffer greatly. They won’t grow as much as they normally would, because their bodies are adapted to different scenarios.

The same goes for keeping the water in the tank clean. If it’s not, then the fish will suffer, they will get stressed, and potentially, they won’t grow as much as they normally would.

So keeping the water in the tank clean is one of the more important things you can do to boost the growth of a discus fish. That can be done with a good filter, but you’ll also need to change the water in the tank regularly.

3. Food and Diet

It’s very important that you feed the fish nutritious foods that will have enough nutrients that will allow them to grow. Proteins are important, but so are other nutrients that allow growth.

You’ll need to make absolutely sure you feed them the best types of foods for growth. Flakes and pellets can be a good source of food, but only if you feed them high-quality foods and pellets. Alternatively, you will need to ensure they get enough of other types of food.

They like meaty foods, such as bloodworms and other similar types of food. These foods will provide enough protein for the fish to grow, and they will also develop brighter colors in the long term.

Keep a good variety in the diet, and don’t feed the fish too often or too rarely. Try to keep a good schedule for feeding. Ideally, this would be 2 times per day, and up to 5 times per day when the fish are still small.

4. Crowded Tank

If the tank is overcrowded, the fish would not have enough comfort to move around, and this can stunt its growth greatly.

The fish’s body will adapt, and they will stop growing in order to adapt to their surroundings better. When there are too many fish in the tank, the fish might feel stressed out, so they will be impacted negatively by this factor.

Also, they simply won’t have enough space to survive comfortably. And they will need to stop growing in order to survive comfortably in a congested environment.

5. Genetics

Sometimes, fish are just not meant to grow large. Just like other animals, fish are genetically conditioned to grow up to a certain size, and they won’t be able to grow over that size, no matter what you do.

If the fish is destined to grow large or small, you won’t be able to do too much to help them grow or help them become larger. Sure, you can try to take some measures, but it won’t probably make that much of an impact.

Some fish are just destined to be smaller, and you shouldn’t be discouraged because it’s probably not your fault if you’re doing everything else right in the fish tank. Just follow the rules and make sure everything else is in check – you can’t do much more than that!

How to Speed Up Growth Rate of Discus Fish Fry

Here’s what you can do to speed up their growth quickly.

1. Offer Them Enough Space

The first thing you need to ensure is the fish get enough space in the tank. That’s one thing you should make sure of before you really buy the fish.

Consider how many fish you intend to keep, and make sure you buy a large enough tank for the fish (50 gallons is enough for one discus fish).

2. Clean the Water and Ensure Good Water Parameters

Another thing you simply must do at all costs is to ensure the water is clean at all times. This is done by a good filter, but you also need to change the water at times.

Keeping good parameters is also key. To support the high-temperature demands of these fish, you might need to buy a heater.

3. Keep Water Temperature Hot and Stable

Again, a heater will serve you very well here, especially if you live in a colder area.

4. Good and Balanced Diet

We’ve already discussed this – make sure you give them the right types of food, but also the right amounts of food.

Keep the diet balanced, and varied. You can feed them pellets and flakes, but also feed them live and frozen foods at times.

When Do Discus Fish Reach Their Full Size?

You can expect the discus fish to reach their full size at about 2.5 years of age. You need to make sure you give them everything needed up to that point so they can grow as much as possible.

After that age, they probably won’t grow too much anymore. When the growth stops are directly affected by genetics, most of the time.


Discus fish can reach up to 8 inches in height and up to 6.5 inches in length. They can become relatively large fish.

But if you don’t give them the right conditions to grow, their growth will be stunted. So you must do everything needed to ensure they grow as much as possible and reach their potential.

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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