How Big Can Goldfish Get?

fisherman holding a beautiful goldfish

Have you ever thought about how big can goldfish get? Goldfish can grow up to 12 inches (30 cm) long in their natural surroundings. However, these sizes are rarely seen in captivity because many factors can slow their growth.

Goldfish are freshwater fish in the Cyprinidae family of the Cypriniformes order. Goldfish may be regarded as one of the most popular aquarium fish and are widely kept as pets in indoor tanks because of their bright colors and the way they move.

In this article, we’ll talk about the factors, like the size of their tank and the genes that affect how big a goldfish can get.

You might want to know how long goldfish live here

Let’s get to it now!

How big do goldfish get in the wild?

In the wild, goldfish can grow up to 18 inches and weigh up to 3 pounds. On the other hand, the typical length of a goldfish living in its natural environment is only about 12 inches long.

The size of a goldfish living in the wild is determined by several factors, including genes, nutrition, and the quality of the water in which it lives.

Giant oranda goldfish
Giant oranda goldfish / Image Credit: Shutterstock

How big do goldfish get in captivity?

In captivity, goldfish can reach lengths of between 6 and 12 inches (150 to 300 millimeters). On the other hand, some varieties of goldfish, such as the Common Goldfish, can reach a size of up to 18 inches in length during adulthood.

When kept in captivity, the size of a goldfish can vary widely depending on the species of goldfish, the size of the tank, and the level of care given to the goldfish.

Factors that affect the size of goldfish:

Several factors that can influence the size of a goldfish, including the following:


When it comes to the size of a goldfish, genetics play a vital part as a determining factor. It is well known that some goldfish varieties, such as the common goldfish, can grow far more prominent than others. This is because, over many generations, they have been bred specifically to produce larger offspring.

It is essential to select a breed of goldfish that is well-known for its size to ensure that it will develop into a massive fish throughout its life.

Tank size

The size of the tank is one of the most significant factors that will determine how quickly your goldfish grow up and how big and healthy they will be.

Goldfish are energetic swimmers requiring a large amount of space to swim around.

A goldfish will not have enough room to develop to its full potential if it live in an aquarium or pond that is too small for them to swim and live comfortable.

The minimum size required for a single goldfish is a tank that holds 20 gallons of water, but it is advised that larger tanks be used when housing numerous goldfish.

Why tank size determines how big can goldfish get?

Space to swim: Goldfish are active swimmers who require a lot of space to swim in because they require a lot of room to move around.

If the aquarium is too small there will be insufficient room for them to swim and exercise, leading to various health issues affecting their growth rate.

Quality of the water:  Goldfish produce an incredible amount of waste; because of this, it is essential to have a big enough tank to hold all the waste produced.

A small tank will not be able to keep up with the generation of waste, which can lead to a decrease in the water’s quality and concerns with the health and the goldfish’s size.

Stress:  Overcrowding and inadequate water quality are two sources of stress that can affect goldfish. Your goldfish may become stressed and develop health issues due to overpopulation and poor water quality if they are kept in a tank that is too small, reducing the growth potential of goldfish.

Water quality

Water quality is one of the most critical components in maintaining healthy goldfish growth.

Goldfish are extremely sensitive to changes in the water quality in their environment and can become unwell quickly if the water is not appropriately kept.

The following are some of the many things that can affect the water’s quality:

Temperature: the ideal environment for goldfish is water that ranges from 68 to 74 degrees Fahrenheit. Your goldfish risk becoming disoriented and losing their appetite if the water in their tank is too cold. Your Goldfish growth patterns may change if the water in their tank is too warm.

pH: Goldfish thrive in water with a pH ranging from 6.5 to 8.0, and this range should be maintained. Too high or low pH value of your water can affect your goldfish growth rate. Your goldfish may suffer skin problems and have trouble breathing if the pH is too high in their environment.

Ammonia:  Goldfish produce a poisonous byproduct called ammonia during their normal metabolic processes. Your goldfish run the risk of becoming ill or perhaps passing away if the water contains an excessive amount of ammonia which is not an Ideal condition for goldfish growth.

Nitrites: Nitrites are created as a byproduct during the decomposition of ammonia. Nitrites, much like ammonia, are incredibly harmful to goldfish.

Nitrates: Nitrates is the result from the chemical reaction that breaks down nitrites and ammonia. In high enough concentrations, nitrates can still be damaging to goldfish, even though they are not nearly as poisonous as ammonia and nitrites.

Oxygen: Oxygen is essential to the goldfish’s respiratory system and in every goldfish growth stage. Your goldfish could become stressed and suffer health problems if the water lacks enough oxygen.

Feeding and Nutrition

The growth of goldfish is highly dependent on the quality of their food and nutrition. Omnivores consume plant and animal matter, and goldfish are no exception to this rule.

A variety of foods, including the following, should be included in a goldfish’s diet to maintain good health and reach the maximum size of goldfish.

A food that is both well-balanced and of excellent quality, consisting of pellets or flakes and occasional treats, like bloodworms or brine shrimp, will give the necessary nutrients for their growth.

A goldfish can become obese or malnourished due to overfeeding or a diet deficient in critical nutrients. This will have an adverse effect on the rate of growth in goldfish.


You may have to introduce some toys to their habitat, and you can allow your goldfish to get some much-needed exercise.

Goldfish can be stimulated with toys, which will encourage them to swim around and investigate their environment.

You will find a wide selection of toys from pet stores, allowing you to pick out some suitable for the dimensions of your goldfish.

The following is a list of some examples of toys that you could put in the tank of your goldfish:

Floating balls: If you want your goldfish to swim more, providing them with floating balls is a fantastic way to do so.

They can also conceal food, which is a great way to keep your goldfish amused and occupied for longer.

Sinking pellets: If you want to give your goldfish mental stimulation, feeding them sinking pellets is an intelligent way. They will have to exert effort to find the pellets, keeping them busy throughout the process.

Mirrors: If you want to entertain your goldfish, consider getting some mirrors. They frequently approach the mirror to interact with their reflection.

Plants: Plants can provide areas for your goldfish to explore and places to hide, depending on the type of plant. They can also help to improve the water quality of your tank.

You can assist in keeping your goldfish active and entertained by providing them with toys to play with in their tank. They will experience benefits to their general health and well-being, and their growth rate will not be impeded.

Goldfish World Championship CIPS 2019 – Aquarium Co-Op​

Common problems with goldfish growth

Stunted growth

Goldfish often struggle with a condition known as stunted growth. It happens when the fish is not given proper care, is not given enough food, or is kept in an environment that is too small to grow into its maximum size potential.

Several factors, including excessive crowding, poor water quality, and inadequate nutrition, can cause stunted growth.

Disease and Infections:

Goldfish growth can be stunted by some illnesses and infections, some of which may be sensitive to the fish and affect its growth rate.

Fish can get weakened from common diseases such as fin rot, parasites, or bacterial infections, impacting their growth and overall well-being. Disease and infections can also be among the Factors affecting goldfish size.


The rate at which goldfish grow into adults can be significantly slowed by obesity. Goldfish can gain excess weight and become obese if they are overfed or consume a diet high in fat and carbohydrates.

The following is an explanation of how obesity influences the growth rate of goldfish:

Slow Growth: Overweight Goldfish often have slower growth rates than their leaner counterparts.

When a goldfish is overweight, excess fat builds up in its body, slowing its overall development and leading to health problems. Because of the added weight, the fish’s internal organs and skeletal structure are put under stress, making it more difficult for them to grow at a healthy rate.

Deformities:  Obesity is a factor that can contribute to the development of deformities in goldfish.

The fish’s skeletal system may become deformed due to the tension caused by the fish’s excessive weight.

These abnormalities include spinal curvatures and bent spines. Deformities might make it more difficult for the fish to grow and can also affect its overall health.

Decreased Lifespan: Obese goldfish are more likely to suffer from health issues and have a shorter lifespan than goldfish that maintain a healthy weight. Because of the strain placed on their organs and the suppression of their immune system, they are more likely to be infected.

Several illnesses, such as fatty liver disease and swim bladder abnormalities, can be caused by obesity.

These conditions can further hinder their growth and shorten their longevity.

Popular Goldfish Varieties and their growth Size

The table below represent Popular Goldfish Varieties and their maximum growth sizes, so In the event that you have chosen to set up a goldfish tank, you can choose from the following list of goldfish species, knowing the maximum sizes at which they can grow will help you make a better decision:

Goldfish VarietiesMaximum sizes they can grow
Common goldfishThis species can reach 4-14 inches. Environmental and nutritional factors will greatly influence this fish’s mature size.
FantailThey have a thick body and a double tail that is easy to spot. They grow to be about 6 to 8 inches (15 to 20 cm) long, based on how well they are cared for and their genes.
CometOne of the largest goldfish kinds, they can reach 12-14 inches (30-35 cm).
Black Moor Black Moor goldfish are black with protruding eyes. They grow slowly to 6-8 inches (15-20 cm).
OrandaDistinguished by its prominent head growth, known as the “wen.” They often grow to be 8-12 inches (20-30 cm) in length, with the wen contributing to this.
RyukinThey  grow to 8 inch – they are semi-aggressive fish species that is more difficult to tolerate in a shared tank
Watonai10-12 inches. This uncommon, extraordinary breed can grow up to 19 inches in an outdoor pond.
ShubukinGoldfish of the Shubukin variety range in size from 9 to 18 inches, making them ideal for large outdoor ponds. If kept in a home aquarium, they will never exceed 6 inches in length.
large size shubunkin goldfish
Large size Shubunkin goldfish. in cold freshwater aquarium / Image Credit: Shutterstock


Q1. How big was the biggest goldfish?

Answer: A gigantic orange goldfish named “The Carrot” weighing 67 pounds 4 ounces (30.5 kilograms), is the world’s biggest goldfish. In 2019, British angler Andy Hackett caught the fish at Bluewater Lakes in France.

Q2. Can goldfish grow as big as koi fish?

Answer: Although goldfish and koi fish are in the same family, they are different species. Goldfish can get pretty big, but they usually don’t get as big as koi fish, which can grow more than 3 feet long, while goldfish, on average, can reach 12 inches in length.

Q3. Can a goldfish outgrow its tank?

Answer: Yes, goldfish can get too big for their tanks if they don’t have enough room.

Q4. Can goldfish continue to grow throughout their lifespan?

Answer: The first few years of a goldfish’s life are usually when they grow the most. As they get older, though, their rate of growth goes down. Their end size is affected by both their environment and their genes.

Q5. Do goldfish eat other fish?

Answer: Yes, goldfish can eat other fish. Being omnivores, goldfish consume both plants and animals. Goldfish will consume various wild tiny fish, insects, and crustaceans.

Q6. How big do goldfish get in a 10-gallon tank?

Answer: Goldfish kept in a 10-gallon tank won’t likely grow to their full potential and may even become stunted.

A 20-gallon tank is the minimum size for a single goldfish. However, larger tanks are advised for multiple goldfish.

Q7. How big can goldfish get in a 75-gallon tank?

Answer: In a 75-gallon tank, goldfish usually grow between 6 and 12 inches long. Some breeds, like common goldfish, can get much bigger, though.

The size of a goldfish in a 75-gallon tank will depend on many things, such as the breed of goldfish, how well it is cared for, and how much space is available


After reading through this guide, “How big can goldfish get?” you could see a wide range of possibilities regarding the size of a goldfish, including the breed, the level of care provided, and the availability of space. Generally, goldfish can reach lengths between 6 and 12 inches when kept in an aquarium or pond with adequate space.

Certain varieties, like the common goldfish, can get quite a bit bigger as they age.

You can ensure that the various factors that affect goldfish growth are adjusted to a favorable state, which will make your goldfish reach its maximum growth potential.

If you find this guide helpful, please subscribe to our newsletter for more updated content.

Related post: 25 Popular Types of Goldfish (For Beginners with photos)