How BIG Do Goldfish Get? (Supersize your Goldfish)

How Big Do Goldfish Get

My goldfish, Goldie, turned 10 years old last week. That’s a long time to have a pet, but it has taught me something very interesting… how big do goldfish get?

In the wild, goldfish can regularly grow upto sizes of 12-14 inches in length. In captivity, there are a number of factors that can affect growth rate, including genetics, tank size, environment quality, and diet. Most goldfish will reach the 6-8 inch mark in length.

Goldfish are members of the carp family. Native to East Asia, they were first kept as pets over 1000 years ago by the ancient Chinese.

Since then, they have grown in popularity to be the most commonly kept fish worldwide, due to their low maintenance needs and stunning color.

Not too long ago, goldfish were regularly kept in small fishbowls, yet they can grow to enormous sizes in the wild.

So, what’s causing this vast difference?

There is also a common myth that goldfish can stunt their growth if they are kept in a constricted environment. Is this true? If so, how large can goldfish get in the right environment?

Read on to find out!

Before purchasing any goldfish, you must do your research to ensure you are offering the best environment for them to thrive.

How can I get my goldfish to grow to full size?

The largest goldfish ever recorded was an impressive 18.7 inches long!

The heaviest goldfish ever weighed was found in a lake in Greenville, South Carolina, in 2020. The giant creature was spotted during a routine fish survey and tipped the scales at a whopping 9lbs!

Many of us have had pet goldfish that have only reached 3 inches long, so what is going on?

The main reason for the vast variation in size is the general care and diet that is offered.

Fish are strongly influenced by their environmental conditions, which is why it is so important to ensure you have the correct equipment before purchasing your goldfish. A fishbowl is no longer considered to be acceptable for these beautiful animals, as it does not fulfill their complex needs.

The myth that goldfish only grow to the size of their tank is only partly true….

The stunt in growth can be caused by numerous environmental factors and often suggests that their welfare is being compromised. The fact is, that if the environment is not right, goldfish will most likely die of illness or stress before they can reach full size.

Let’s run through the main factors now:


This first one may seem a little odd but genetics are actually a big influencer in how large a goldfish can grow. There are around 200 species of goldfish worldwide, all with their own specific needs and characteristics.

That’s a lot of genetic diversity!

Although most of these species have the capability of growing fairly large, the difference between species can vary considerably.

Another factor you need to consider is the size capability of an individual fish. Just as with dogs and cats, you can get runts of the litter with fish too. With these fish, it won’t matter if you have the environment perfect, they simply won’t grow that big!


Tank size

Fish kept in tanks that are too small, often suffer from intense stress that can stunt their growth, cause diseases, and even result in a shorter lifespan.

If you are considering buying a goldfish, you will need to first do your research on the needs and potential size of the species you are looking to purchase. Any tank that you buy, should take into account the size your goldfish species will be when it reaches adulthood.

As a general guide, your fish tank should be at least 4-5 times the length of an adult fish, even if you are purchasing a juvenile.


Number of fish in your aquarium

The more fish you have in your aquarium, the more competition there will be for space and food.

This will certainly have an impact on the size your goldfish can grow!

You also need to be wary of the species you mix in the tank as certain species can get on well together whereas others will fight.

Bottom-dwelling fish such as Plecos and loaches make the perfect tank mates for goldfish as they do not share the same water space.

Other popular fish to house with goldfish include tetra’s, danios, and minnows. However, be aware that large goldfish can sometimes target smaller fish species so make sure you keep an eye on them.

Just in case!


Environment quality

Goldfish will not grow if they are kept in a dirty environment, as this will make them much more susceptible to developing diseases and physical deformities.

This is the reason that fishbowls are no longer seen as acceptable housing for goldfish, because they cannot be set up with an effective filtration system and do not allow for sufficient aeration in the water.


Water temperature

Goldfish are considered to be cold-water fish, which can easily lead to the misconception that they can live in cold water.

This couldn’t be further from the truth!

The term cold-water simply means that certain species prefer COOLER temperatures than more tropical fish species.

In reality, the ideal temperature for your goldfish is between 71 and 75 Fahrenheit (21-24 degrees Celsius).

To help your goldfish grow to its full size, it is vital that you consider all of these factors and regularly check your aquarium for any issues.

You can purchase aquarium test kits from most pet stores and online, which are a great aid for any budding aquarist!

Each kit comes with a range of simple tests designed to check certain water parameters in your tank, including nitrate and ammonia levels. These parameters are often invisible to the naked eye but can be extremely detrimental to your fish.


How quickly do goldfish grow?

Goldfish grow rapidly in their first year of life so it is essential that you purchase a tank large enough to accommodate this.

Depending on species, a goldfish fry can double its’ size in less than three weeks if tank conditions are ideal!

Once they become a few months old, the growth rate will slow dramatically to around one inch per year.

Unlike other pets commonly kept in the home, goldfish grow steadily throughout their entire lives, so in theory older goldfish will be larger than their younger counterparts. However, it is important to note that the growth rate is dependent on the factors noted above, as well as species type.

It is good practice for you to determine the type of goldfish you have, in order to ensure they have the correct environmental conditions.

So let’s run through the more common varieties now:

Common Goldfish

These are the most popular breed of goldfish due to their stunning coloration and ease of care. They can be identified by their shorter body and tail, compared to other breeds.

Common goldfish are best suited to outdoor ponds as they can tolerate colder temperatures well.

They are incredibly hardy fish that can live for up to 40 years and reach 12-14 inches in length.


Comet Goldfish

These fish are also common as pets and can easily be recognized by their long flowing tails.

Comet Goldfish need a lot of room to prevent their delicate tails from damage, so they also do well in ponds. This breed can reach 10-12 inches at maturity.


Fantail Goldfish

Fantail Goldfish are one of the fancy goldfish breeds, alongside other species such as the Ryunkin, Oranda, and Black Moor.

They get their name from their long, fan-like double-tails.

These fish are more susceptible to the cold so should be kept in an indoor aquarium or an outdoor pond that is heated. Fantail Goldfish can grow up to 8 inches in length.


What should I feed my goldfish?

Aside from the factors mentioned above, diet is also extremely important in ensuring your fish is healthy and able to grow to full size.

In the wild, goldfish will eat pretty much anything that will fit in their mouths!

Common dietary items include everything from algae and small insects to crustaceans and other fish, so you should offer a varied diet in captivity too.

The bulk of your goldfish’s diet should be a high-quality goldfish flake or pellet food. However, as omnivores, it is also essential that you offer vegetables too. Good options include courgette, peas, kale, and cucumber.

Always remember that different goldfish species have slightly different nutritional requirements. However, as a general guide, you should aim to feed your goldfish at regular interviews 2-3 times a day.

You may need to feed juveniles slightly more often as goldfish will do most of their growing in the first year of life.

As goldfish need feeding regularly, you can consider investing in an automatic fish feeder, particularly if you are prone to forgetting feeding times or you plan to go away for a few days.

Simply program in your feeding times and let the machine do its job!

Saying that, if you plan to use an automatic fish feeder on a regular basis, do make sure you check it regularly to ensure it is working correctly.


Conclusion: How Big Do Goldfish Get?

Did you think goldfish were boring? I certainly did… until I started keeping them. Having the basics down, there’s more to learn, and as any goldfish hobbyist knows, one of the most common questions they get is, “How big do they get?” So I decided to give you an answer that’s crystal clear.

That was our guide on how big do goldfish get. We brought up everything, from the varieties to their care and feeding. If there is one thing we hope you take away from this article, it’s this: your fish deserves a bigger tank!

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