July 29

What is the Maximum Size of a Goldfish? Potential Size vs. Average Size


Most goldfish keepers expect their 2 Inch goldie to grow only a few inches and live comfortably in a 20-gallon tank for their entire life. But it becomes a pleasant surprise when they grow to large size of 10 inches. Because goldfish are a notable member of the carp family, they contain the genetics for large growth. Common carp can grow to massive 30 inches in the wild. It leads many people to wonder how big can goldfish get.

In this article, we will be answering this question in detail. 

big goldfish

How Big Can Goldfish Get? 

Goldfish size depends on a number of factors. We will discuss some of the factors in a later section. For now, let’s look at the most important factor – the environment. 

How Big Can Goldfish Get in a Tank?

Well, it depends on the type of tank. Most goldfish species will stop growing once they’re one or two inches tall if the aquarium is small. If you keep yours in a bowl, they may not even reach that size. 

However, 2 inches is not a standard size for a goldfish. They are capable of growing to a much larger size. Because of their genetics, they are meant to grow throughout their life span. Their growth gets stunted only when they are kept in an unsuitable environment. 

So, if the tank is small and living conditions are bad, it will prevent the goldfish from growing to their full potential. It will also shorten their lifespan. However, if the tank size is adequate and you take proper care, expect your goldfish to grow as much as 6 inches long in a fish tank. 

How Big Can Goldfish Get in a Pond?

Goldfish have excellent endurance. They can endure harsh weather pretty well, which makes them thrive well in an outdoor pond. Generally, different goldfish species can grow anywhere from six to 12 inches ( or even bigger) in a pond. 

However, it also depends on the type of goldfish, their size, and suitable environmental conditions of the pond. Ideally, a goldfish pond should be 50 square feet on the surface. If it’s a smaller water garden, it needs 50 to 500 gallons. 

How Big Can Goldfish Get in the Wild?

According to National Geographic, goldfish can get around 7 to 16 inches long in the wild. They can weigh 0.2 to 0.6 pounds, but in some rare cases, they can even top 5 pounds in the wild. 

Why do Goldfish Grow so Big in the Wild?

There are several reasons goldfish grow so big in the wild.  

First, their environment is totally different. Oxygen supply is abundant. There is enough water and natural filtration that goldish can’t contaminate the water. Plus, they don’t have any natural predators. 

So, they have everything they need to continue growing, and there’s no stopping them. That’s why some of the largest goldfish ever caught measured over 18 inches in length and 9 pounds in weight. 

How Big Can Goldfish Get in a Lake?

Very big. As previously mentioned, goldfish can get around 7 to 16 inches or even more in a lake. Culum Brown, a professor at Macquarie University, says goldfish can reach up to 23 inches if released into a large pond. Though typically, their lifespan is 10 to 20 years, if the conditions are right, they can live up to 30 years. 

Because of this, goldfish in lakes have become a big ecological problem in the USA. 

Giant Goldfish

    5 Factors that Determine How Big Goldfish Can Get

    We discussed the impact of the size of the tank (or lake) above. Now let’s look at other factors that determine how big (or small) your goldfish can get. 


    No matter what you feed them or what you do to make living conditions better, different types of goldfish will grow differently. This is because of genetics. A poorly bred fish will not grow as big as a quality goldfish from a popular breeder.

    An inbred goldfish will be smaller by nature, and no environmental factor or care will make them grow larger than possible. Most pet stores breed goldfish on a mass scale. They provide little care to the quality of the goldfish. Rather, they focus on quantity. A goldfish bred in such circumstances has poor genetic lineage from birth.

    Likewise, the type of goldfish also influences the size. Some types are genetically inferior in size. For instance, the comet goldfish will grow smaller than the regular goldfish.  Similarly, the pompon goldfish will always be smaller than the comet goldfish and so on.


    Like any other living organism, giving them the best goldfish food will impact their growth. They grow bigger when they get the proper nutrition that includes a high proportion of proteins and alkaline substances instead of tropical fish food. If there are out in the wild, they can get enough bugs, vegetable matter, and smaller fish to care for nutrition.

    However, if they are kept in an aquarium, you should be careful not to overfeed them. Overfeeding often pollutes the water and leads to constipation in goldfish. In contrast, some people feed their goldfish less to avoid polluting the water. This means the fish don’t receive the necessary nutrition, leading to a smaller size.

    Therefore, you should try to keep a balance between the two.

    Treatment During First Year of Life

    As you can see in the chart below, goldfish grow the most during their first year. In just six months, expect your pet goldfish to grow to about 2 inches if you provide them with the best living conditions. This includes excellent water conditions, lots of space to roam, a great filtration mechanism, a suitable water temperature, and a nutritious goldfish diet.

    Water Quality

    The quality of your water also impacts how big goldfish can grow. When the water is full of toxins or there are other goldfish tank mates, they cannot develop properly. In such a situation, they must channel all of their strength into survival, leading to stunted growth. You should get rid of any toxins in the tank by regular water changes and recycling. It will improve your water quality and allow your fish to grow big and strong.

    Nitrate levels

    Goldfish can tolerate nitrate levels up to 40 PPM. Any number above is a big no-no – especially for the young fish and the fry. If you find your aquarium’s nitrate levels hovering around 40 PPM, you need to change the water asap. Aquarists believe that high nitrate levels for prolonged periods can inhibit the growth of goldfish.

    Signs of high nitrate levels can manifest in the form of algae blooms and greenish water. 

    How Do I Get My Goldfish to Grow Really Large?

    Depending on the genetics of your goldfish and life parameters. Generally, expect your goldfish to grow to a foot or more in size. However, there is no guarantee. Just be sure to provide the most suitable environmental conditions along with a good diet for optimum growth. 

    The easiest way to ensure the development of your fish is to give them a bigger and better environment. If your fish lives in a fish bowl, upgrading to a filtered tank can dramatically change their size and appearance. 

    For smaller goldfish, 20 gallons per fish tank size is an absolute must. It often requires upgrades if you have more than one goldfish in a single tank. Like most other fish, the bigger the tank, the better it is. Otherwise, goldfish can face serious health issues. Take a look at some common goldfish diseases for detail. 

    However, a bigger aquarium size isn’t always beneficial for fancy goldfish. Most fancies have a precarious grasp of changes in water conditions and neutral buoyancy. Any sudden changes can cause buoyancy issues. Also, ornamental goldfish don’t like swimming large distances, such as in outdoor ponds. Therefore, they benefit from a more controlled environment. 

    Another thing to keep in mind is that goldfish increase in size when they are ready to lay. Keep an eye out for these signs if the goldfish is pregnant

    Once you have the right tank, feed your fish a proper diet, store them nicely and maintain their water chemistry along with regular maintenance, and your goldfish will grow to their optimum length. 

    Wrapping It All Up

    We hope now you know how big your goldfish can get. Watching them grow to adulthood is definitely fascinating and a rewarding experience. We all want to see our favorite pets reach their full length, size, and lifespan. So, knowing what’s possible can help us upgrade the living conditions as they grow. We hope this article has been helpful in your quest for better growth of your goldfish. Thank you for reading. 

    FAQs on How Big Can Goldfish Get

    Do Goldfish Grow to the size of their Tank?

    Yes, that’s true. Even when you keep goldfish in good condition, they will only grow to a size proportional to the size of their tank. Unlike other fish, they excrete hormones that signal to estimate the size of the water body and the number of fish in their environment. It prevents them from running out of resources. But, it can also inhibit their growth. 

    How Old do Goldfish Get?

    With optimal conditions for goldfish keeping, the fancy goldfish can live as long as 20 years or even longer. But their lifespan reduces drastically to 5 to 10 years if released in a pond.

    On the other hand, Some varieties of common goldfish can live longer for 25+ years in the wild. 

    How Fast do Goldfish Grow?

    Goldfish grow fast. They grow about one inch per year. Their growth is rapid during the first few months of their life. And unlike other species, goldies can continue growing throughout their lifespan. 

    Do goldfish have a 3-second memory? 

    We often hear this as one of the fun facts about goldfish. But, it’s not true at all. It’s a myth that goldfish have a 3-second memory. They are capable of remembering things for a very long period. Experts believe common goldfish can remember things for at least three months. Besides, they also have a sense of time, and they can learn routine fairly quickly. 

    How big can comet goldfish get?

    The comet goldfish is one of the largest goldfish species. They can easily reach a length of 12 inches when mature. 

    How big can feeder goldfish get?

    Feeder goldfish can reach a length of 12 to 14 inches on average. They can grow much larger in the wild.

    How big can black moor goldfish get?

    Blackmoor is a fancy fish that can grow as tall as 8 inches when mature. Its males are smaller than females.


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