How Fast Do Goldfish Grow? Goldfish Growth Guide

It can be daunting for some goldfish owners to realize how fast their goldfish grows. Goldfish are often marketed as easy, beginner fish, so you may not know what you’re getting into when buying one.

Did you start out with a small bowl or tank, only to realize it’s too small for your goldfish? Or, maybe you didn’t buy one yet, but you’re trying to prepare yourself.

How fast do goldfish grow? This depends — tank size, water temperature, water quality, and food can all have an impact.

This is not an easy question to answer. There are many things that control the growth of your goldfish. Genetics, of course, is a factor, but how you take care of your fish plays a bigger role in their growth.

When cared for properly, an adult goldfish will grow about one inch per year (2.54 cm). Yet, they will grow even faster than this when they’re babies! That’s right, taking on a goldfish is an enormous task — pun intended — so it’s best if you go into this hobby prepared.

Baby Goldfish Growth Rates

What is the goldfish fry growth rate? Let’s break it down:

Week 1

When they first hatch, goldfish fry will be a meer 3/16” (4.5 mm). In just 3 days, they will have grown to 0.2 in (5mm) in length.

Week 2

During week two, baby goldfish will reach about 0.27 in (7 mm) in size and will have a defined tail fin.

Week 3

In the third week, goldfish will have reached about 0.43 inches (11 mm) in length, and you will begin to notice a dorsal fin.

Week 4

By week four, goldfish growth will start to slow down. They will only reach a size of about 0.53 inches (13.5 mm). Still, you will now notice that your goldfish has developed ventral and anal fins.

Week 5

Your goldfish will reach about 0.63 inches (16 mm) in length, and their fins will be fully developed. Their coloration will also begin to darken.

Week 6

Your goldfish will reach about 0.7 inches (18 mm) in length and their eyes will become more noticeable.

Week 7

By week 7, your goldfish will have grown to about 0.86 inches (22 mm) in length.

Week 8

By week 8, your goldfish will reach about 1 inches (25.4 mm) in length.

Week 9

This is the point at which your goldfish’s growth will drastically slow down. But, as we mentioned, goldfish can still grow up to 1 inches (2.54 cm) in a single year which is quite impressive.

Genetics & Care

The size of your aquarium tank is going to play the biggest part in the growth rates of goldfish. Food, water temperature, and water quality can affect their growth as well.

How big a goldfish can grow also depends on the kind of goldfish. There are hundreds of varieties of goldfish, so none of them look or develop exactly the same. Still, many goldfish varieties can grow up to 14 inches long!

What Controls A Goldfish’s Growth?

There are many things that determine rates of goldfish growth besides its genetics. If you want your goldfish grow big and healthy, keep these things in mind:

Tank Size

Likely the most important aspect of your goldfish’s growth is the aquarium tank size. Many people don’t realize that buying a goldfish tank that is too small will severely stunt the growth of your goldfish.

Many people also buy into the myth that goldfish will only grow to the size of their aquarium. This is partially true, but it’s not quite accurate.

A goldfish’s body will stop growing so that it doesn’t outgrow its aquarium tank. But, it’s possible that its organs will continue to grow, leading to many problems.

Whether this is entirely accurate is still up for debate as there hasn’t been much research conducted on it. Some fish experts say it’s true, while others say it’s a myth.

Either way, we know that when a goldfish lives in a bowl, it usually doesn’t live for more than a few years. When kept properly, a goldfish can live for 10-15 years.

It’s okay to start off small when you buy a baby goldfish, but you’ll have to upgrade over time. A 10-gallon aquarium is the absolute minimum you should provide for a baby goldfish.

As an adult, the smallest tank you should have is a 30-gallon. Ideally, you’ll have 40-50 gallons for your goldfish. For each additional goldfish you want to house, you should add an extra 10-gallons.

Water Temperature

Goldfish are very adaptable and can survive in a wide range of temperatures. But, the keyword to keep in mind here is “survive”. Just because they can live in some extreme temperatures, doesn’t mean they’re going to thrive there.

Most fancy goldfish can survive in temperatures as low as 40° F (4.4° C). Common Goldfish can live in temperatures even lower than that. Likewise, goldfish can survive in tropical temperatures, but they don’t like the heat.

Low temperatures cause your goldfish’s metabolism will drop, which slows their growth. When they’re kept in waters that are too warm, they become stressed. Their metabolism increases, causing too much pressure on the body, leading to disease.

For your goldfish to grow optimally, you should keep their aquariunm tank set between 65-72° F (18°- 22° C). Anything higher or lower than this is likely to stunt your fish’s growth.

Water Quality

For a goldfish to be healthy and grow properly, it needs to live in healthy water. Goldfish produce a lot of waste, so you have to keep on top of their water quality.

For a healthy tank, your water parameters should look like this:


Feeding is another important factor that determines how fast a goldfish grows. They are omnivores, so they need a healthy, varied diet.

Their main diet should consist of a healthy goldfish flake or pellet. You should supplement this with regular feedings of veggies or aquatic plants. They should also get the occasional protein snack. Blood worms or daphnia are good choices. As is being fed brine shrimp.

Besides feeding them the right things, you also need to know how much to feed them. A good rule of thumb is to feed as much as they can eat in about 2-minutes.

If you don’t feed them enough, your goldfish will become malnourished, and they will not grow properly. You should feed your goldfish twice a day for about the first year. After that, you can drop feedings down to once a day.

Fish Overcrowding

If there are too many fish in the tank, your goldfish won’t have enough space to swim around or grow. This can cause them to become stressed which lowers their immune system. This often leads to illness and disease, which then causes slowed growth.

How To Tell If Your Goldfish Is Stunted

Whether there are any physical signs that your fish is stunted remains up for debate.

Many experts believe that a goldfish’s organs will continue to grow even after its body has stopped. Some goldfish have appeared to back-up these claims, having swollen or deformed bodies.

But, whether this is due to overgrown organs or some other health defect, isn’t quite known.

Can A Stunted Goldfish Continue To Grow?

This depends on how old your goldfish is. If you realize that your goldfish is stunted early on, then you can likely correct the issue before it’s too late. Upgrade the tank, fix the water, and feed them more food. They should bounce back and go on to become healthy adults.

But, if they are already adults and this has been occurring for a long time, your fish will likely remain stunted.

If you fix their environment, it should encourage growth. But, their new growth will never reach the potential it could have if you’d fixed the problem earlier.

We’ve covered the most important goldfish growing facts. But, you may still have some questions.

How Long Does It Take For Goldfish To Grow Full Size?

How long it takes a goldfish to grow full size depends on the type of goldfish and the environment it’s living in. Goldfish that are naturally bigger will take longer to reach their full potential. Also, if the fish is living in unideal conditions, then it will grow more slowly.

But, goldfish are indeterminate swimmers. This means they continue to grow until they die. So, if the goldfish is living in a large tank with good water conditions, it can grow to 14-15 in (35.5-38.1 cm) before it dies.

How Do You Make Goldfish Grow Faster?

There’s nothing you can do to make your pet goldfish grow fast. But, if you keep it in a healthy tank, your goldfish will continue to grow at its proper rate.

Some goldfish keepers believe feeding your goldfish more high-protein meals can encourage growth.


When kept in good conditions, your goldfish should grow about 1 in (2.54 cm) a year. To keep your goldfish happy, house it in a large tank. Watch the water parameters and the temperature, and keep your fish well fed.

Do all this, and your goldfish should become big and strong in no time.

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