How big do goldfish grow? Some can be massive!

People often think that goldfish only ever grow to be a few inches long. Sadly, this is because most pet goldfish don’t live long enough to grow beyond this. However, with good care, goldfish have the potential to be much larger.

Common goldfish can easily grow to be 10 inches long and fancy varieties can reach 8 inches.

And these aren’t maximum limits! They’re fairly standard sizes, with some fish growing to be even larger…

How big was the biggest goldfish ever?

The wild goldfish pictured below was reported to be 14 inches long.

14 inch long wild goldfish
This wild goldfish measured around 14 inches (Photo courtesy of Buffalo Niagara Waterkeeper)

A pet goldfish in the UK was reported to be 15 inches long.

And the biggest goldfish ever recorded – the official world record – was a gigantic 18.7 inches!

These potential sizes are why we encourage all of our readers to buy a good sized tank or to keep their fish in a pond. It’s vital to ensure they have plenty of room.

While it is true that fish will become stunted if kept in smaller tanks, we consider this practice to be cruel and bad for your fish. You should always give your pets the space they need. This allows them to grow to their full potential.

Why do they get so big?

Genetics is a factor. Some individuals simply have the potential to grow bigger than others depending on their genes.

However, all healthy goldies could grow to several inches long if they receive the right care.

Goldfish will naturally grow to a large size when they are well looked after and given the right conditions to live in. These conditions include plenty of pond or tank space, good water quality, warm water temperatures and a supply of nutritious food.

Goldfish Growth Rate

The average growth rate of a goldfish is about one inch per year.

Baby goldfish grow very rapidly in their first few months. Then their growth rate slows as they get older.

There are ways to make your goldfish grow faster, but remember: you should always aim to provide your fish with the best possible care.

You shouldn’t try to stunt their growth to keep them small or overfeed them to make them grow. You will only end up harming them.

That said, if you really want a big goldfish – and you want to make them grow faster – there are some things you can do to safely influence your goldfish’s growth rate.

Next, we’re going to explore the five factors that influence growth rate.

How do you make goldfish grow faster?

The key to making goldfish grow faster is a good diet combined with lots of tank space, warm water temperature and good water quality.

It also helps to choose fish with the right genetics. Though you will need to go to a specialist breeder to have any chance of knowing whether your particular pet had large parents!

Let’s look at the five factors that influence goldfish growth rate in more detail.

#1: Nutrition

Having a good diet is very important.  Serious breeders feed goldfish fry a high protein diet of live foods, such as micro-worms and baby brine shrimp. This stimulates growth and helps to produce the largest fish.

The runts in a spawn, who do not get as much food as the others, will not reach the size of their siblings. Because of a poor diet when they were young, some fry will never reach more than a few inches long for the rest of their lives.

A nutritious diet plays a big part in growth rate throughout your fish’s life. This is why feeding good food is a must.  Live foods and veggies, in addition to a good protein staples, like pellets, can help your fish grow.

However, you must be careful to never overfeed them! Overfeeding will pollute your water and cause your fish to become constipated.

#2: Tank Size

Many goldfish have the potential to reach an impressive size, but then their owners buy an undersized tank or add too many fish.

Not having enough tank space will stunt your fish’s growth. Their activity will be restricted, meaning they get less exercise, and growth inhibiting hormones will build up in a tank that is packed with too many fish.

Sadly, stunted goldfish are permanently impacted and the damage is irreversible. You therefore need to give your fish plenty of space from a very young age and throughout its life.

#3: Temperature

Temperature plays a big role in growth rate.

Goldfish kept in warmer water temperatures consume more oxygen, eat more food and are generally more active. All of this helps them to grow to a large size.

Water temperature in the mid-70s Fahrenheit (mid-20s Celsius) is ideal.

#4: Genetics

As we mentioned earlier, the growth potential of your fish is limited by their genetics.

Unfortunately, unless you are a goldfish breeder, you really can’t do much about this one!

All you can do is buy your goldfish from a quality breeder, rather than a chain store. This will give you a better chance of finding a fish with good genes and which hasn’t already been stunted by poor conditions.

#5: Water Quality

Maintaining good water quality is not only vital to your fish’s health, it plays a role in their growth too.

When toxins are present in the water, goldfish cannot grow normally and must channel their strength into surviving. You can get rid of these toxins by cycling your tank and doing weekly water changes. This will improve your water quality and allow your fish to put more of its energy into growing big and strong.

How big is your fish?

Add a comment to let us and other readers know how big your largest goldfish is.

1 thought on “How big do goldfish grow? Some can be massive!”

  1. My goldfish is 4.5 inches in a 55-gallon tank. He gets feed 3 times a day, enjoys the flakes. He also eats meal worms every wensday for protein. He has one tank buddy, a betta 2 inches. I was surprised they didn’t fight.

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