Goldfish Growth Chart – How Big Do Goldfish Get?

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If you’ve never had a goldfish before, now it’s time to find out more about this extremely popular fish species.

Goldfish are amazingly diverse, hard, generally peaceful, and can grow to different sizes, depending on their environment, species, water conditions, diet, and other factors. These will not only influence the goldfish’s maximum size but growth rate as well.

That being said most of the goldfish’s growth rapidity and the maximum size is influenced by genetics. Knowing that goldfish can live around 10-15 or even 20 years, it’s safe to say that this species ranks as a slow grower.

Unlike other fish species that can grow absurdly fast (the Oscar, for instance, can pack one inch every month for the first year), goldfish grow slowly. Painfully slowly at times, causing people to wonder whether there’s something wrong with them.

But let’s dive deeper into the subject to assess the goldfish’s growth rate along with the facts that influence it.

Goldfish Growth Stages

It’s worth noting that the goldfish’s growth speed and maximum size varies depending on numerous factors. We will assess these in detail in today’s article for a clearer and more accurate picture of the matter.

This means that the data in the following table may not represent your actual experience with your goldfish.

Goldfish Age Goldfish Size
1 month 0.9 – 1 inch
6 months 1.5-2 inches
12 months 2.8 inches
18 months 3.5 inches
24 months 4 inches
3 years 5 inches
4 years 6 inches
5 years 7 inches
6 years 7.5 inches
7 years 8 inches
8 years 8.5 inches

As you can see, the goldfish’s growth rate is more accelerated during its first months of life, after which it drops over the years. That’s because the fish’s metabolism drops with age, causing the goldfish to slow down.

It’s also important to note that goldfish will experience significant physical changes during their first 2-3 months of life, as they progress from fry to juvenile.

These changes include:

  • Doubling in size within the first week, from 0.2 inches to 0.4
  • The same growth rate remains for the second week, as the fry nearly doubles again, provided it gets nutritious meals along the way
  • Goldfish fry will develop fins by the end of week 3, allowing them to move faster and more precise through their environment
  • The growth rate will slow down by the end of week 4; at this point, your goldfish should measure around 0.9 to 1 inch
  • After week 4, the goldfish will grow at a relatively steady rate, given proper food and adequate water conditions

How Long Does It Take for Goldfish to Grow Full Size?

It’s almost impossible to answer this question conclusively. That’s because too many factors weigh in, based on which the answer will change dramatically.

Here are some of them to consider:

  • The goldfish strain – Goldfish fall into 2 major categories, fancy and slim-bodied. There are several differences between them, with the most notable one relating to their genetic makeup. Slim-bodied goldfish are closer to wild goldfish in terms of genetic makeup, while fancy goldfish are the result of human selective breeding. Naturally, fancy goldfish will grow smaller and slower than the others. Slim-bodied goldfish may take years to reach their full size, growing at a pretty steady rate. Fancy goldfish, especially those living in smaller tanks, may reach their full size in about 6 months to a year.
  • Diet – Goldfish are omnivorous, so they consume both plants and animal-based protein. While they require a balanced and mixed diet to satisfy their nutritional needs, it’s the animal protein and fat that boosts their growth. A healthy diet should consist of 30% protein and 12% fat for optimal growth rate and healthy development. Improper diet will hinder the goldfish’s growth rate, aside from causing a variety of health problems along the way as well.
  • Environmental factors – Here we include factors like the tank’s size, temperature, water parameters, and tank mates. Goldfish require a lot of open space to feel comfortable and fitting water parameters to boost their growth. It’s also worthy of mentioning that having aggressive tank mates will affect their growth rate and maximum size due to the stress they may experience.

The conclusion couldn’t have been clearer: your fish’s growth rate depends a lot on you.

Why are My Goldfish Not Growing?

It may be difficult to notice hindered growth rate in mature goldfish, primarily because their growth rate is difficult to measure. Adult goldfish may pack up to an inch per year if that. They will grow even slower under certain conditions.

That being said, the best time to detect your goldfish’s hindered growth is during the fry phase. That’s when the goldfish is supposed to grow faster. If they seem to stagnate, something may be wrong.

Among the factors that could hinder your goldfish’s ability to grow we include:

  • Insufficient space – Goldfish fry will do just fine in a smaller tank, maybe 10-20 gallons for several fry during their first week after hatching. But you better move them into a larger environment soon. Juvenile goldfish require around 30 gallons of water if they’re living by themselves. Every other goldfish should increase the tank’s size by at least 10 gallons. This will provide the goldfish with enough room to remain comfortable, active, and experience a healthy growth rate.
  • Overcrowding – If you overcrowd your goldfish, expect them to remain smaller and grow slower than normal. At the same time, overcrowded goldfish display increased aggression towards their tank mates and showcase signs of stress, including hiding, lethargy, and predisposition towards violence. Overcrowding also affects water quality, since goldfish are notorious poop producers, capable of overwhelming their closed environment fast. Don’t keep too many goldfish in the same environment, since they’re not used to living in crowded habitats.
  • Water quality – This is probably the most important factor here, due to the extreme implications coming on the side. Poor water quality won’t only hinder your goldfish’s growth, but it can kill them fast as well. Goldfish will produce a lot of poop, capable of poisoning the tank water fast. Lacking adequate tank maintenance can be a death sentence for your goldfish since it will incentivize the dangerous buildup of ammonia and nitrites. To prevent that, weekly water changes and frequent tank cleaning work are necessary to keep water parameters within acceptable limits.
  • Overfeeding – This is the number one problem related to goldfish’s poor development. Overfeeding is common among goldfish, especially with novice keepers who don’t know how goldfish’s digestive system works. Goldfish don’t have stomachs, they only have a digestive intestine separated into several areas, one of which is the mid-gut. This area stores the food temporarily to allow the digestive system to extract vital nutrients. This biological conformation prevents the fish from eating too fast or too much. It’s one of the reasons why overfeeding causes goldfish to experience constipation, hindering their growth rate and risking complications along the way.
  • Water temperature – I should say this is a no-brainer for anyone with basic knowledge of fish biology. The problem is simple: goldfish require environmental temperatures around 68 to 74 F. These values may differ slightly, depending on the goldfish’s species and health status. The problem is that, if the temperature goes below the acceptable threshold, the goldfish’s metabolism will slow down dramatically. This will cause the goldfish to experience lower growth rates, depending on how low the temperature is. Most species of slim-bodied goldfish will even enter hibernation during the cold season, capable of withstanding below-freezing temperatures. During this time, their metabolic rates will be so slim that they won’t grow at all; so, you have that.
  • Disease or parasites – If your goldfish is sick, its growth rate may be hindered, depending on the condition’s nature and severity. Viral infections are pretty damaging in this sense, especially since they can spread to other goldfish fast. If one of your goldfish shows signs of parasitic or bacterial infections, consider quarantining the fish to protect the rest of the population. Immediate treatment is vital to prevent the disorder’s spread and ensure faster and safer recovery.

As you can see, a lot of things can go wrong along the way, especially if you’re not used to monitoring your goldfish constantly.

Many of these problems are more common among novice fish keepers due to their lack of experience and being overwhelmed by their goldfish’s needs.

How to Make Goldfish Grow Faster?

Based on what we’ve discussed so far, I believe there are several things you can do to boost your goldfish’s growth significantly.

  • Increase the tank’s size – This is the most important factor, no matter what anyone might say. If you’ve ever heard the notion “the larger the tank, the bigger the goldfish,” you know what I’m talking about. It’s true that goldfish will grow as much as their environment allows them to. It’s why pond goldfish will grow a lot larger than tank ones. If you have fancy goldfish, provide them with sufficient space to boost their growth rate and maximum size.
  • Offer nutritious meals – Goldfish fry require more protein and fat compared to adults. This will boost their growth rate significantly and sustain their higher metabolic rates during their first few weeks of life. You can cut down on the protein past their first 2 weeks after hatching since adult goldfish don’t require as much protein as the fry. Long-term, I suggest personalizing your goldfish’s diet and offering a variety of foods, like veggies, daphnia, brine shrimp, and even vitamin and mineral supplements if necessary.
  • Ensure optimal genetic makeup – Sometimes, no matter what you do, your goldfish will simply refuse to grow to the desired size. This is partly due to the fish’s genetic predisposition since not all fish have the same genetic makeup. This is why I recommend only purchasing goldfish from reputed sources, that guarantee the fish’s good health and genetic prowess. As much as that’s possible, of course.
  • Keep the water within the optimal parameters – Monitor the temperature, prevent the buildup of ammonia and nitrites, and clean your goldfish’s tank regularly. You should also avoid overfeeding and ensure proper water oxygenation. These things will keep your goldfish in a safe and clean environment, boosting their growth and preserving their health over the years to come.

What Size is the Largest Goldfish?

The reports are contradictory on this topic. To answer in relative and generalist terms, goldfish will mostly grow up to 18 inches in the wild, in optimal conditions.

In captivity, consider yourself lucky if your goldfish reaches 10 inches in a pond. Tank ones will only grow several inches, no more than 6.

There are several underlying reasons for such differences, but the most relevant one is the difference between an open versus a closed environment. Wild goldfish grow larger for multiple reasons, including increased water oxygenation, more food availability, and larger space.

The fish’s natural habitat provides a variety of challenges, keeping the fish at the top of its game, physically and mentally.

It’s extremely difficult, if not impossible, to replicate these conditions in a tank or even a pond. Although, the latter seems more feasible, which is why pond goldfish grow larger.

How Big Can Goldfish Grow in Aquarium?

The answer depends on the goldfish’s species, age, health, genetic makeup, diet, and the tank’s size.

Depending on these factors, expect your goldfish to grow up to 6 inches at most. However, a more realistic size would be in the neighborhood of 1.5-2.5 inches for most goldfish.

Goldfish Max Size

If you’ve decided to start a goldfish tank, here are some available goldfish species to consider and their respective maximum sizes:

Goldfish Type Maximum Size
Common goldfish 4 -14 inches – Yes, this species’ maximum size can vary that much. Environmental factors and nutritional setup will play a massive role in determining this fish’s adult size.
Fantail 6-8 inches – This goldfish requires a minimum tank size of up to 20 gallons.
Comet 4-12 inches – The comet’s size is heavily influenced by its environment. Expect this goldfish species to reach its maximum size within 3-4 years.
Black Moor 8 inches – A great goldfish species both for indoor tanks and outdoor ponds.
Oranda 8-12 inches – A larger goldfish species with an impressive head growth, often covering its eyes. It’s the result of heavy selective breeding, making for a beautiful specimen.
Ranchu 5-8 inches – The ranchu goldfish can remain comfortable in 10 gallons of water. You only need to add 5 more gallons for each ranchu you introduce to the environment.
Shubukin 9-18 inches – Shubukins are larger goldfish, primarily used for outdoor ponds with a lot of space available. They will only grow up to 5-6 inches in indoor tanks.
Ryukin 8 inches – A semi-aggressive fish species that are a little trickier to accommodate in a community tank.
Watonai 10-12 inches – This is a rare, but exceptional breed, capable of growing up to 19 inches in an outdoor pond.

As you can see, there are numerous goldfish species to consider, some of which can be pretty exotic and unique.

Their lifespan and overall size and growth rate are heavily influenced by their environment. Keeping them in an indoor tank will naturally hinder their maximum size.

Conclusion

If you’ve decided to invest in a pair of goldfish, I recommend researching your favorite strain thoroughly before purchasing it.

Learn about its environmental requirements, space needs, dietary preferences, and any other aspects that may help you provide better care in the long run.

By doing so, you will be able to harness all of the specie’s potential in terms of growth, coloring, lifespan, and overall personality.

avatar I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.

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