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The Goldfish Gazette, Issue #013 -- Goldfish Growth Rates
February 01, 2015

Goldfish Care Tips and Guidelines

A Free Monthly Resource For Goldfish Enthusiasts
January 2015
Issue #013

In this issue
Goldfish growth rates
What's new on the Website

Goldfish growth rates depend entirely on the conditions the goldfish are kept in, and the amount and quality of food you feed them.

Goldfish Growth Rates

I was recently asked how old a one inch goldfish was.

Apart from not specifying what variety the goldfish was, or if the measurement referred to total length or body length, it would still be nearly impossible to tell the age of the goldfish unless you actually saw the fish. Even then it would still be very difficult.

If the goldfish had been kept in the optimum growing conditions, and it was a single tailed variety, it could have been 1 month old.

If the fish had been kept in a small bowl and fed dried foods, it could have been 3 years old.

Five Factors Determine Growth Rates

Five different factors all have an impact on goldfish growth rates. They are:

1. Water conditions

2. Space and water surface area

3. Water temperature

4. Amount and type of food

5. Health of the fish

Any one of the above factors can dramatically affect the growth rate.

Water Conditions

Partial water changes are critical for young goldfish. They are eating all the food you can provide, and producing large amounts of waste.

Goldfish fry growth rates will be severely affected by polluted water.

Space and Water Surface Area

If you don't install some system of filtration and aeration, then you need to allow 24 square inches of surface area for each inch of fish.

Filtration systems have the duel benefit of keeping the water clean as well as increasing the amount of water exposed to the air.

You still need to make those regular partial water changes.

Water Temperature

Water temperature has a huge influence on goldfish growth rates. A 5oC increase can double the growth rate over a 30 day period.


When goldfish are small, they can be fed almost continuously. They eat until they are full, process what they have eaten over an hour or so, then start eating again.

It is much safer to feed live food during their early development because it won't quickly spoil in the warmer temperatures fry need to be kept in.

Fish Health

This is one of the more critical factors that affect goldfish growth rates.

If they get some ailment due to polluted water, or catch flukes from their parents, they stop growing. Even if cured, they never catch up the lost time it takes to cure them.

They also never seem to thrive as well as fry that never got sick during their early growth stages.

Because so many factors affect how fast a goldfish grows, anyone buying a fish under 50mm or two inches in body length out of the breeding season can only guess what the age of the fish is. Experience does help, but the buyer should only purchase fish that are displaying excellent health.

To read more on Goldfish growth rates click here...

What's New On The Website

Goldfish Growth Rates

For more on goldfish growth rates I've created a page that has some graphs that show how fast Black Moor fry should grow in their first 8 weeks, and another showing an average growth rate over 12 months for fish kept outdoors all year round.


Comments? Ideas? Feedback? I'd love to hear from you. Just reply to this e-zine and tell me what you think, or what topics you want covered.

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