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How Big Can Goldfish Get in Your Tank? And Will They?

There are known records of goldfish growing to enormous sizes. But how big can goldfish get in an aquarium? After doing some research, here’s what I found.

Quick Answer

Goldfish in tanks grow to between one and three inches in length, usually to no more than six inches. They can grow to 14 inches in the wild. Goldfish kept in aquariums may not grow to their maximum size due various reasons including secretions, limited space, poor water conditions, and more.

If you want your goldfish to actually grow big and healthy, make sure to keep reading. We’ll go through everything you need to know!

How Big Can Goldfish Get – And Will They?

In the wild, your common goldfish can grow to around 12 or 14 inches in size. There are even some specimens that have been recorded as being even longer. Currently, the world record for the longest pet goldfish is a walking 18.7 inches, which is absolutely massive.

goldfish on blurry background

However, in an aquarium, goldfish will usually never reach the same size as they would in the wild. Goldfish kept in aquariums usually grow to around one or two inches, with three inches being fairly rare, and in very rare instances, some might grow up to six inches long. As you can tell, this is significantly smaller than a goldfish in the wild.

The main point here is that goldfish kept in aquariums are usually several times smaller than their true potential maximum size that they would achieve in the wild, and there are a few good explanations for this. Let’s move on and figure out why exactly goldfish kept in tanks are generally smaller than ones living in the wild.

Why Do Goldfish in Tanks Stay Smaller Than in Ponds or in the Wild?

There is one main cause which is thought to be responsible for goldfish kept in aquariums staying much smaller than those in the wild, and this has to do with the secretions that they release into the water. 

There are two types of secretions that goldfish release into the water which tend to impact their growth rate and size. This is especially the case in an enclosed environment.

One of the secretions responsible for this phenomenon are pheromones, with the main one being somatostatin. The other secretion released into the water by goldfish which can affect their size in an enclosed environment is GABA, otherwise known as gamma-aminobutyric acid.

Because the goldfish always swim in that same water along with their secretions, they reabsorb a lot of them back into their own systems.

Although I’m not going to get into the biology or chemistry of it here, both of these substances can cause the growth rate of a goldfish to be stunted, and a decrease in their overall maximum size. 

It is thought that this is a natural response of a goldfish that is growing in a small environment. It’s almost like a natural growth stopper that prevents goldfish from outgrowing and enclosed space.

Second, it is also believed that this phone non occurs because male goldfish want to stunt the growth of other male goldfish, therefore reducing competition for food and mates. 

Although these secretions are very important and likely the major cause of goldfish in tanks not growing to their maximum size as they would in the wild, there are also other causes believed to be behind this.

Other Factors That Affect Goldfish Size in Aquariums

While the above factor is believed to be the main cause of goldfish in aquariums generally not growing as large as they would in the wild, there are also other factors to consider, so let’s take a quick look. 

Generally speaking, for any fish cap in a captive environment to grow as large as possible, it needs to be living in the proper conditions and be well maintained.

Water Conditions

One of the most important factors that can contribute to the slowed growth and smaller size of goldfish in tanks is water quality and the overall water conditions.

Water quality in general really comes down to cleanliness, and this has a lot to do with the presence of uneaten fish food, decaying plant matter, and fish waste. 

Although, it is not those substances in themselves that are harmful to your goldfish and their overall size, but rather the ammonia and nitrates they release.

Ammonia and nitrates are very harmful to fish in a variety of ways, and stunted growth is just one of the results. Therefore, you need to make sure that the water is as clean as possible.

Water Parameters

Something else that can severely impact the growth rate and maximum size of your goldfish are various water parameters, mainly pH levels and water temperature. 

Goldfish do best in waters ranging between 68 and 74 degrees Fahrenheit, or roughly 20 to 23 degrees Celsius. More on that can be found here on the site: goldfish water temperature.

If the water is any cooler than this, it will slow down their metabolism and cause slower growth, and water any hotter than that may cause increased levels of stress and can also stunt growth.

On that note, goldfish also require the pH level, otherwise known as the acidity of the water, to be somewhere between 6.5 and 7.5, with a completely neutral 7.0 being best. If the pH level is outside of this range, it may also cause stunting growth.

The Diet

The other part of the equation here is diet. Just like human beings, for a goldfish to grow big and strong, it requires the proper nutrients. 

One of the most important components of a healthy diet for a goldfish is protein, with anywhere between 30% and 40% protein being ideal.

If you give your goldfish food with less protein than 30%, it will stunt their growth. Goldfish also require adequate amounts of carbohydrates, some fats, and a small amount of minerals for proper growth.

How to Ensure That Your Goldfish Grows to Maximum Size

Now that we figured out what causes goldfish to stay relatively small in aquariums, let’s take a quick look at some of the best tips you can follow to ensure that they grow big and strong.

A Large Tank

Seeing as goldfish appear to be directly impacted by the secretions that they release into the water, it serves to reason that the larger the tank is, the less these secretions will affect them. 

Once again, the secretions they release into the water are thought to be a result of a natural instinct or mechanism to stop the goldfish from outgrowing their tank size.

Therefore, the larger the tank is, the more spread out in the water these secretions will be, ultimately reducing the effect that they have on the growth and size of the fish. 

A good size tank for a common goldfish that is between two and three inches in length is roughly 10 gallons. More on the best tank size for goldfish can be found here.

A Well-Balanced Diet

To make sure that your goldfish grows big and strong, providing it with a well-balanced diet is important. A good fish food should have around 40% protein, about the same amount of carbohydrates, roughly 10% fats, with the remainder being minerals.

Different fish foods will have slightly different ratios, but this is definitely a good starting point. Remember, protein is perhaps the most important nutrient of all in terms of goldfish growth and size.


Now that I’ve provided you with all of the most necessary tips, let’s see just how big you can get your goldfish to grow.

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