How Fast Do Goldfish Grow: Monitoring Your Pet’s Maturity

how fast do goldfish grow
Japanese Fighting Fish is reader-supported. When you purchase through one of our links we may earn an affiliate commission (at no extra cost to you).

Last Updated: July 28, 2022 by Flora Gibbins

The growth rate of a pet goldfish is affected by many variables. The growth rate depends on a healthy environment which includes; water quality, tank size, water temperature, proper nutrition, and other factors.

But how fast do goldfish grow? There is no specific answer to this question. Usually, a pet goldfish is around five to seven inches long. The baby goldfish growth rate is high in the first few weeks after hatching. The growth rate reduces after becoming an adult goldfish. On average, in their adulthood, they grow an inch yearly.

When given good care, goldfish have the potential to grow big and very quickly.

How Large Do Goldfish Get?

In 2003, The Guinness Book of World Records recorded the longest pet goldfish to be 18.7 inches.

The record shows that goldfish can grow big if cared for correctly. But not all goldfish can grow big due to good environmental factors. Because genetics also plays a significant role in growth.

various goldfish in tank

Wild goldfish tend to get big due to their natural environment. Some can get between 12 inches to 16 inches long.

Your Goldfish History

All the variety of goldfish developed over the centuries can trace their lineage back to the Crucian Carp. The wild carp can be traced back to Eastern Asia. Having a common ancestor makes goldfish have typical behavior and habits. People chose the wild goldfish for their appearance and ability to grow big.

Goldfish Characteristics

Because of its adaptability and commonality, the goldfish is the most kept fish pet. It can tolerate extreme environmental conditions.

There are wide varieties of goldfish that vary in color and appearance.

As cold water fish, wild goldfish thrive well in their natural environment in temperatures between 50 – 60 degrees, while fish in the aquarium thrive in temperatures between 65 – 75 degrees.

different species of goldfish

During the breeding season, females spawn multiple times.

The sticky eggs get to stick on the gravel below during development.

Varieties Of Goldfish

There are many kinds of varieties of goldfish. The following are the most common varieties.

Common Goldfish

The common goldfish is hardy and can live in an aquarium or a pond. The common goldfish has a stout body and can grow eight inches more with proper care.

The common goldfish come in many colors and combinations, such as red, orange, brown, and blue.

If given space, this variety can grow big and have a lifespan of over ten years.

Comet Goldfish

comet goldfish in a fish tank

The comet goldfish is what many people think of when they hear the name goldfish.

Apart from its sleek and long fins, in appearance, they look like the common goldfish. They come in a variety of colors, such as silver and orange. They can quickly get to 12 inches or longer.

Comets are bred commercially for sale to pet shops because they are naturally prolific breeders.

Fantail Goldfish

Fantail goldfish fall in the group known as fancy goldfish. Their body is rounded and egg-shaped. They can quickly get between six and eight inches long.

The fantail goldfish is easily noticeable because its tail has two top and bottom fins.

Fantails are typically white to red in color or multicolored.

Goldfish as a Pet

colorful goldfish swimming in tank

It is the most common type people tend to keep. It can be an excellent first-choice pet for your kid.

Your pet begins its journey as a goldfish fry and measures about 0.2 inches. They start to look like fish in about two weeks and measure approximately 0.6 inches.

It is essential to ensure you provide the fish with a safe and adequate environment and quality food. Favorable environmental conditions also call for quality water, enough space, and freedom from disease predisposing factors.

Goldfish Growth Journey

The goldfish fry measures about 0.2 – 0.4 inches in the first week. In the second week, it grows to approximately 0.6 inches. The fins also start to develop. They can move around, feed, and measure 0.8 inches in the third week.

goldfish floats in aquarium

Since they are getting closer to maturity, in the fourth week, the growth rate reduces, and they measure 0.9 inches. In weeks five and six, they have a complete fin set that measures 1 inch. They also start taking their adult shape.

In the seventh week, they measure about 1.1 inches. In week eight, they measure about 1.25 inches, and their weight has dramatically increased compared to the first week.

After week nine, it has increased in size and has a mature shape.

In about six months, your goldfish will have reached about 2 inches. It will be over 3 inches in its first year with proper nutrition and the right environment.

Factors Affecting Goldfish Growth

Goldfish growth is affected by the following factors. The following factors can affect how fast your goldfish can grow.

Water Quality

two goldfish in a fish tank

Water quality can have a significant impact on your goldfish. For a goldfish to live longer and healthy, it requires excellent water quality.

Polluted water can cause health complications and slow the growth of your goldfish.

Overcrowding can result in the water being poor in quality due to the excess waste production.

To ensure water quality is perfect, provide frequent water changes. Also, ensure the water filter sponges are clean and not clogged. They ensure the water condition is stable and clean.

It would be best if you also carried out frequent water tests to determine the chemical compounds in your water tank. Waste from goldfish causes low oxygen levels and releases toxins such as ammonia, nitrites, and nitrates. A build-up of such can affect the growth of your fish. Usually, the water pH should be between 6.0 and 8.0.

Factoid: In this area of concern, you have to make sure that everything affecting your goldfish pet is well maintained and properly monitored. Diseases could easily set in and affect the well-being of your aqua buddy if you’re not careful! One of these illnesses is fin rot and you can learn more about this here — Goldfish Fin Rot: Identify The Symptoms & Cure Immediately!

Water Temperature

fish tank water temperature thermometer

A consistent temperature is an essential factor for goldfish. The ideal temperature for a goldfish is between 71 to 75 Fahrenheit.

Cooler water causes your fish metabolism to slow down. Due to the slow metabolism, the growth rate slows down. If the temperatures are too high, the metabolism will increase. High metabolism causes them stress resulting in sickness and thus reducing the growth rate.

Moderate temperatures will make the goldfish consume more oxygen and eat well. As a result, goldfish growth is increased.

Tank Size

A large tank is vital for the growth of your goldfish. It enables your goldfish to move and exercise freely. A small tank can inhibit your pet fish from getting to its full potential size.

A small overcrowded tank can negatively impact your goldfish’s health. A small tank also prevents the fish from exercising and thus causing development problems and stunted growth.

The recommended tank size is, for one goldfish, a 20-gallon tank. For an extra fish, one should add 10 gallons.

Since goldfish produce a lot of waste, a big tank will provide enough space for the dilution of ammonia.


Proper and nutritious feeding is essential for the growth of goldfish. For proper nutrition, you should consider food high in alkaline and protein. A high protein diet such as brine shrimp encourages the growth of goldfish.

Feeding a good diet is necessary since nutritious food plays a vital role in goldfish growth.

You should ensure you don’t overfeed your fish since it is dangerous. Overfeeding can lead to fish constipation, and the excess can decompose to waste and increase ammonia levels.

Ensure you maintain a feeding schedule that is similar daily.

Feed your goldfish pet the recommended portion two to three times daily.
Factoid: Goldfish, like any other aqua pets you have or planning to have, are not choosy when it comes to fish food. Just make sure to do proper food apportioning to avoid overfeeding and polluting their aquarium water. One popular favorite fish food is bloodworms. Read all about them here — What Are Bloodworms: We Investigate This Squiggly Fish Food.

Frequently Asked Questions

How big do goldfish get?

In a small tank, a pet goldfish grows between five to seven inches long. While in a large tank, the goldfish’s growth rate can be quick and grow up to 14 inches long.

How to grow goldfish faster?

Ensuring proper care and a nutritious diet is the best way to ensure your goldfish grow faster.

How long does it take for a goldfish to be at full size?

Goldfish growth is indeterminate, and they keep on growing until their death. In a healthy environment and a large tank, they can grow up to 14 inches.


One cannot determine how fast your pet fish can grow because a goldfish’s rapid growth depends on various factors.

The major factors determining how fast your goldfish will grow are how well you maintain the tank and how big it is. You are aware that during the first few weeks, your goldfish will increase, and after that growth rate slows. However, the growth rate can be increased by following the above factors.

Leave a Comment

Your email address will not be published. Required fields are marked *