How Fast Do Goldfish Grow?


Goldfish make wonderful pets. They are intelligent, adorable, and do not require a lot of attention. Yet, raising these friends with fins from tiny fry to mature fish might be a challenging task.

Likewise, the answer for “How fast do goldfish grow?” is hard to tell since the matter depends on numerous variables. This article summarizes their development stages, everything you need to draw your conclusion for the query.

And in the latter part are a bunch of tips and foundation knowledge to give your goldies the best home ever!

Goldfish Growing Rate From Hatchlings To Juveniles

Below are the details on the weekly development stages to know how fast goldfish grow?

  • Week 1

Incubation usually takes 04 days. To be specific, the process depends on the temperature (69-75° Fahrenheit). If the water temperature is warmer, the incubation time could be shorter, only 02 days and a half to 03 days. If the temperature is too low, the egg might need 6-8 days to hatch.

Upon hatching, the newborn will be around 3/16 inches (4.5 mm) in body length. By Day 3, the fry will grow in size, approximately 7/32 inches (5mm) long. In this period, you can feed them infusoria or brine shrimp nauplii.

  • Week 2

From Day 8-14, the fry size should increase by 40%. It means a total of 9/32 inches (7 mm) in body length. Also, at this stage, you can see its caudal fins. These fins are to determine if the baby is a single-tailed or double-tailed goldfish.

In this stage, the best food recommendation is mosquito larvae (wrigglers). Nauplii of Daphnia pulex and brine shrimp are also perfect choices.

  • Week 3

From Day 15-21, the fry will go through rapid growth. You may even observe a 50-57% increase in body size! The fry will also develop dorsal fins and grow longer, measuring 7/16 inches (11 mm).

Food options for this week are similar to the previous one. You may feed them brine shrimp, mosquito larvae (wrigglers), and Daphnia pulex.

  • Week 4

From Day 22-28, the growth rate starts to drop. You may spot the fry developing its anal fins and ventral fins. During this stage, the fish should fully develop their dorsal fins.

Contrary to the whopping increase of 50% at week 3, the fry’s body only grows by about 20-23% at week 4. Its length will be approximately 17/32 inches (13.5 mm). In this stage, the fry can eat 2-week-old wrigglers, along with their usual diet of nauplii of brine shrimp and Daphnia pulex.

  • Week 5

From Day 29-35, the color of the fry may get darker. Its body may increase around 19-20%, which means 5/8 inches (16 mm) long. All fins are well-developed, and you can notice its scales.

Some food recommendations include nauplii of brine shrimp and Daphnia pulex, full-grown wrigglers. You may also feed the baby goldfish some gel fish food to add nutrition and carbohydrates.

  • Week 6

From Day 36-42, the growth rate will decline significantly. The fish body may only develop around 12.5%, measuring 22/32 inches (18 mm) long. Its skin will get darker, and the eyes start to protrude a bit.

From now on, the fry has become juvenile. It will be able to digest goldfish gel, flakes, and some veggies. A mixture of their usual diet with invertebrates and some fish flakes would be a perfect choice.

  • Week 7

During this week, the fish keep growing at a slow pace, measuring 7/8 inches (22 mm) long. From this week onwards, you should maintain a high carbohydrate diet to boost its growth.

  • Week 8

From Day 50-56, the juvenile fish may increase by 15%, meaning 1 inch (25.4 mm) in length. Even the latest bloomers should have a darkened color and protruding eyes at this stage.

  • Week 9 And Beyond

After the first two months, goldfish will develop at a slow and steady speed. Usually, it would gradually stop growing when the fish is six months old. From this stage onwards, try your best to give your goldie the optimum conditions for its growth.

What Factors Affect Goldfish Growth?

Multiple factors determine the growth of goldfish. The major ones are water conditions and their diet. This fish species is ammonia-sensitive. They are also unable to live in polluted water where the oxygen level is low.

In addition, the fish will release growth-impeding hormones into the tank over time. Thus, you need to frequently change the water inside the aquarium to ensure your fish is still thriving.

Diet is another major factor to improve the growth of your goldies. As the fry grows greater, you can gradually let them have more food to help prevent nutritional problems.

Most people choose commercial fish food for convenience. But goldfish are voracious eaters and need a variety of food. Make sure you add some fresh food like veggies and live worms to their diet from time to time. These are a great source of minerals and vitamins for your yellow friends with fins!

Read more: How long do goldfish live

How To Boost The Growth Rate?

Juvenile goldfish need at least 5-10 gallons per fish to reach their maximum size. The fish will demand much more space as they grow larger. Thus, preparing a spacious tank in advance is never a waste of resources.

Water at 65-75°Fahrenheit is an ideal environment for growing goldfish. Goldfish enjoy chill lakes and ponds. But they might abstain from food if the surrounding temperature drops below 55°Fahrenheit.

Last but not least, let your fish bathe in light for 12 hours a day. Fish that do not receive adequate daily light may become colorless. They might also shed their scales and refuse to eat.


That’s all about our answer to the question, “How fast do goldfish grow?”. Raising goldfish is never an easy task. Still, this is also a great chance to practice responsibility and discipline.

We hope the article has provided you with helpful information to boost the growth of your goldfish fry. Have a great time with your swimming friend!

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