How big do goldfish get?

Silverado is a great example of how big do goldfish get

As prominent members of the carp family, goldfish contain the genetics for very large growth. There are many giant goldfish claims that actually turn out to be orange koi, a very close cousin of the goldfish. Depending on the goldfish type in question, how big do goldfish get?

How big do comet goldfish get?

Comet or common “feeder” goldfish have the greatest potential for large growth. Yes, these include those fish given out at fair events. Many carp species, including goldfish and koi, have almost exponential potential for growth throughout their lives, depending on their access to life resources such as space and food. Restricting your fish’s space to “the size of their container,” is the same as stunting. This also applies to withholding food to improve maintenance or limit growth. Your fish can be fed regularly, just with a lower protein diet, and still maintain their overall health and wellness. Do not use your laziness in doing proper maintenance as an excuse not to feed your fish.

In captivity, we have seen comet goldfish grow up to the size of a dinner plate (14″). Meet Silverado:

Silverado is a great example of how big do goldfish get

This comet had his own 100 gallon tank to accommodate his large size. He was in his teens when he passed away. Other than a mass next to his eye and some wavering water chemistry, he had a very good life. But he is a prime example of one of those little fair goldfish thriving at life.

How big do goldfish get in a pond?

Many goldfish living in outdoor ponds can get very large as well. Access to lots of food and space usually allow goldfish to grow a foot long or more. Ponds mixing koi and goldfish and feeding high protein or growth food often leads to goldfish being mistaken for koi.

How big do fancy goldfish get?

Depending on the variety, fancy goldfish can also get very large, but not as large as long-body, comet goldfish. We have seen a Ryukin 10″ long and almost the same circumference. Due to their genetic restrictions, most fancy goldfish do not get larger than 6-8″ long, which may or may not include their ornate fins.

When growing monster fancy goldfish, extreme caution should be taken in making sure they grow slowly. Sudden growth can cause buoyancy disorders where their swim bladder cannot accommodate their mass and lead to common fancy goldfish buoyancy disorders.

Due to their limiting genetics, fancy goldfish varieties usually do not grow very large

What is the record for largest goldfish?

Most of the “Largest Goldfish” records are actually koi, a different species from goldfish. The world record for the longest goldfish was set for 47.4 cm (18.6 in) in March 2003.

How do I make my goldfish grow to full size?

Depending on your fish’s genetics and life history, they might not grow to the size you expect. Certainly, most goldfish could potentially grow to a foot or more, but nothing is guaranteed. For all fish, be sure to provide the right environment and diet for the best life possible.

The easiest method to ensuring the health of your goldfish is to provide a bigger and better environment. Upgrading from a horrific bowl to a filtered tank has brought about our most dramatic changes in goldfish size and appearance. For small goldfish, a tank size of 20-gallons per fish MINIMUM often requires upgrades to significantly larger tanks (see one fish in 100-gallons above). For most fish, including goldfish, the bigger the tank, the better.

A bigger tank is not always beneficial for fancy goldfish. Many fancies, with a precarious grasp of neutral buoyancy, can have issues with tank upgrades that are significantly deeper than their previous tank, causing increased hydrostatic pressure and buoyancy issues. Fancy goldfish do not do great when having to swim large distances, such as in outdoor ponds, and may benefit from a more controlled environment with less drag and pull on their long fins.

Once you have the proper tank, be sure to feed your goldfish a proper diet, store it properly and maintain their water chemistry with regular maintenance.

Why do goldfish grow so big?

Goldfish are members of the carp family and descend from Crucian carp. The carp family of fishes is a very diverse group and well know for their ability for immense growth. In the wild, it is not uncommon for many carp species to be 2-3 feet in length and weigh over 15 lbs. In some areas, carp are farmed for food, but this hasn’t caught on very much in the USA. When given unlimited resources and few predators, goldfish and their carp cousins can grow very large. 

This can cause issues with these fish becoming invasive species, especially if they have been released into an ecosystem that is not usual for them. This happens very commonly when goldfish and koi are “returned” to the wild when owners are unable to keep them anymore due to their unexpected size. If your fish has grown too large for their system, NEVER release them into a wild habitat. This can have catastrophic results on that environment, usually as a result of a large, unchecked predator eating everything in sight.

Koi are another member of the carp family, but descend from the Common carp, a different species. Koi can also easily grow longer than a foot and should never be kept in a small, indoor aquarium. Koi require lots of room to swim and at least 250 gallons per fish, which will increase with the size of your koi. 

When it comes to carp, it’s simply their genetic code that allows them to grow so big. If you fuel this growth with a high protein diet and give them lots of space, you can expect your carp species, koi and goldfish, to grow very large, very fast.

koi size
Koi grown for shows are usually larger, given their aggressively high protein diet at a young age

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