Goldfish Care Tips and Guidelines

A Free Monthly Resource For Goldfish Enthusiasts
July 2017
Issue #043

In This Issue
Goldfish Growth Rates

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Goldfish grow as fast as their environment will allow.

Their growth will stop completely if large water changes aren't made regularly.

Goldfish Growth Rates

Since first writing about Goldfish growth rates in issue 13, I have been reading about another factor that affects growth rates…suppression of growth hormones.

I have intentionally used the words "suppression of growth hormones" because there are two distinct opinions on what causes growth to be suppressed.

The first group believes that if a fish is kept in poor water conditions, it causes the fish’s own growth hormones to be suppressed.

The second group believes that Goldfish release a growth suppressing hormone that if allowed to build up, will suppress even the fish’s own growth.

This is different to other fish species such as White Cloud Mountain Minnows. They are very easy to keep and breed as they don’t eat their eggs or fry. The only problem is larger fry release a growth suppressing hormone that stops younger smaller siblings from growing.

So which group is correct? Perhaps both answers are. The scientific community seems to favor the latter identifying a growth hormone-inhibiting hormone called Somatostatin as the cause.

So how important is this for enthusiasts wanting to grow their fish?

Growth Hormones and Fry

If there are large size differences in a brood, that suggests the larger fry are somehow suppressing the growth of the rest of the fry, but it is usually because the amount of food fed in the first few weeks was inadequate.

When fry reach the juvenile or young adult stage, I have experienced a slow down or complete stop in growth if I haven’t made enough regular water changes. This leads me to the conclusion that once fry become adults, they start releasing growth inhibiting hormones.

Goldfish growth does slow down after they reach adulthood no matter what size they are. This is why in the first 12 months it is so important to give your fry the best possible conditions to grow in as they will never grow as fast again.

Water Change Frequency

Large frequent water changes.

I did an experiment with four Black Moor fry to test how large I could grow them in 6 months, in a small 60 liter aquarium. I fed them heavily with large amounts of daphnia and mosquito wrigglers, and made twice weekly half water changes. These fish attained a body length of 70mm (2 ¾"), which provided answers to several questions.

1. How fast can Goldfish grow?

2. Do frequent water changes make a difference?

3. How much food can fry and juveniles eat?

If I had separated out the four fry earlier, and provided a continuous supply of food, I believe they would have grown even larger.

I was making frequent water changes to remove waste, not growth inhibiting hormones. These were still juveniles so whether they were producing growth inhibiting hormones I don’t know.

The most important lesson learnt was, if large frequent water changes are made, Goldfish grow faster.

Other Factors Determining Growth rates

The 5 original factors I listed that determine how fast fry or juvenile fish grow are still relevant. They are:

1. Water conditions – fry don’t tolerate ammonia or any form of pollution.

2. Space and water surface area – oxygen levels need to be high for Goldfish to process large amounts of food.

3. Water temperature – a 5^oC increase in water temperature can double the body weight over 30 days.

4. Amount and type of food – fry and juveniles need high protein food and often as they eat continuously. The more they are fed, within reason, the faster they grow.

5. Health of the fry – sick fry don’t grow.

In Summary…

To read more on Goldfish growth rates click here…

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