Freshwater Fish

How big do goldfish get? Growth rate for the different types

How big are goldfish? Well, according to the Guinness Book of World Records, the largest pet goldfish recorded to date hails from the Netherlands and measured a whopping 18.7 inches long. Although that size is unusually large, goldfish grow quite large if kept in the right environment and fed a high-quality, balanced diet.

So how fast do goldfish grow? That depends on a number of factors, and if you want to know how to care for a really big goldfish in record time, then you need to read this fascinating article!

The largest goldfish in the world

The world’s largest goldfish that was actually weighed came from the UK and weighed in at over two pounds! Goldie, as the fish was imaginatively named by its owner, lived for 15 years and grew to be five inches tall and just under 15.5 inches long. Despite being kept in a small tank, Goldie’s impressive size can be attributed in part to the excellent care and diet provided by his loving owner.

In Holland, another pet goldfish made it into the Guinness Book of World Records, measuring an incredible 18.7 inches long. Although the fish was never placed on the scale, its weight was estimated to be around three pounds.

Why do they get so big?

In the case of these two record-breaking fish, their impressive size is most likely due in part to the care they received as pets.

Water quality is also extremely influential when it comes to goldfish growth. If the water quality is poor, the growth of the fish will be stunted and they may even develop physical deformities as a result. In addition, a nutritious diet and abundant food will influence.

Average weight of a goldfish

The weight of a goldfish depends on the variety of goldfish and its age. However, on average, a common pet goldfish weighs about eight ounces. When it comes to length, fancy goldfish with their characteristic egg-shaped bodies usually grow to around eight inches in length, while single-tailed goldfish can reach anywhere from ten to 12 inches in length.

So you can see that the world record breaking fish in the UK and the Netherlands were exceptional specimens, rather than the norm.

Goldfish Growth Rate

Goldfish grow about an inch per year, growing most rapidly during their first few months of life. Unlike most other common pets, goldies continue to grow throughout their lives. Goldfish do not grow in spurts, depending on their environment and other factors. For example, a goldfish that lives in an outdoor pond will grow larger during the spring and summer when the water is warmer, and will grow smaller during the winter months when the temperature drops.

How big can goldfish get in the wild compared to those in a tank?

Modern goldfish are generally believed to be descended from the wild Prussian Carp and Crucian Carp that originally came from Central Asia, although these fish are now found in Europe, Asia and North America. Goldfish belong to the Cyprinidae family of fish, along with common carp and minnows.

The Prussian carp grows to an average of 18 inches in length and weighs about 6.6 pounds. The usual color of the species is silver, but they are found in other morphs, including orange and gold, leading them to be mistaken for pet goldfish that have been released into the wild, having outgrown their tanks.

Wild goldfish?

Strictly speaking, there is no wild goldfish. If you ever see a fantail or kite swimming in your local lake, it is a pet fish that has been released into the wild.

So if your pet grows too big for his tank, should you let him loose in your local pond or river?

Absolutely not! First of all, goldfish are considered an invasive alien species that could have a negative impact on the ecosystem into which they are released. Second, a pet goldfish is unlikely to survive long in the wild, as it will most likely fall prey to larger predatory fish such as pike or bass.

koi carp

Koi carp are sometimes released into the wild and some escape commercial farming operations and find their way into ponds and lakes, where they can be mistaken for goldfish. Koi carp can grow to between 24 and 36 inches in length, although some “jumbo” varieties are capable of reaching a staggering 52 inches in length.

Why do wild «goldfish» grow so large?

These relatives of wild goldfish can reach their immense size for a number of reasons. First of all, the water in which the fish live is usually cleaner than that of the closed environment of a home aquarium. In addition, the water is very well oxygenated and is periodically replenished with rainwater.

If the habitat has a good food supply, there is no limit to how much the fish can eat. Once the fish have reached their adult size, there are few natural predators to bother them. Finally, the space available for fish is much more than they would normally enjoy in a home fish tank.

What happens to goldfish in a tank?

There is some truth to the urban myth that the size to which pet goldfish grow is directly related to the size of their tank. In general, pet goldfish grow up to a couple of inches long if kept in a small bowl or tank, and do not enjoy the natural growth spurts of their wild relatives.

There are several reasons for stunting:

  • Goldfish are extremely dirty fish, which quickly contaminate your tank water with waste. If you don’t have an efficient filtration system that is properly maintained, levels of ammonia, nitrites, and nitrates build up quickly in the water, poisoning or shocking fish.
  • Goldies need a varied diet that includes plant matter, algae, and meaty foods as well. A staple diet of flake foods does not provide fish with everything they need for optimal health and strong growth. Compare the diet of a typical pet goldfish to that of a wild carp and you will quickly see the difference.

So, with proper care and the correct aquarium size and setup, there’s no reason your small pet goldfish can’t reach their full 12-inch potential.

How to make goldfish grow fast

The best way to help your pet reach his full growth potential is simply by providing the proper care and diet.


Although the foundation of your fish’s diet should be a high-quality goldfish food, either flake or pellet, goldfish need a varied and properly balanced diet if they are to achieve their full size and lifespan. up to 20 years.

A high-protein diet is important to stimulate growth, especially in juvenile goldfish. Good sources of protein include live or frozen bloodworms, brine shrimp, and daphnia. You can also buy gel foods that contain added vitamins as well as protein sources.

Goldfish are omnivores, so you should include some vegetables in their diet. Blanched zucchini and fresh shelled peas are often well received and are also helpful in preventing constipation, which is a condition that frequently affects goldfish fed a diet containing mostly dry food.

Ideally, you should feed your goldfish two to three times a day, offering enough food for the fish to eat in a minute or two.

tank size

The poor goldfish all too often lives its life in a small bowl or tiny tank, neither of which are suitable for this species. If your pet is going to grow to full size and enjoy a long and happy life, you should provide your fish with a tank that is at least 30 gallons. Add an additional 10 gallons for each extra fish. That means you’ll need a tank that’s at least 50 gallons if you want to keep a group of three goldfish.


Water temperature can affect the rate at which many species of fish grow, including goldfish. For adult goldfish, the ideal temperature range is between 71o and 75o Fahrenheit.

Although goldfish can survive temperatures as low as 65o Fahrenheit, colder water causes the fish’s metabolism to slow down, effectively reducing their growth rate as well. So if you keep your goldfish’s tank in a warm room, its metabolism will speed up, it will use more oxygen, and it will eat more food, and all of these things lead to a faster growth rate.


When it comes to your goldfish genetics, you are sharing food! Buying a goldfish feeder from a pet store or even a specialty fish store does not guarantee that you will end up with a large pet.

If you buy a goldfish from a breeder or enthusiast, you can learn more about the genetic makeup of your fish, and that can give you a better idea of ​​how big you can reasonably expect your pet to grow.

Water quality

Unfortunately, these creatures are extremely dirty fish, so you must have an efficient filtration system in your tank to keep the water clean and free of harmful toxins. Goldfish are intolerant to ammonia, nitrites, and nitrates in their water, so you should test your water weekly to ensure levels are within acceptable parameters.

Do a partial 25% to 30% water change every week and use a gravel vac to remove solid debris and other debris from the substrate. Check filter sponges and cartridges to make sure they are not clogged and make sure the impeller is clean and free to move.

Ideally, the pH of the water should be between 6.0 and 8.0, with a water hardness between 5 and 19o dH.

In conclusion

If you want your pet goldfish to grow to full adult size, you’ll need to provide it with a large enough tank, excellent filtration, and a balanced, nutritious diet. Also, keeping the temperature around 75o will help boost the growth rate of your fish.

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