What water temperature do goldfish need?

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My forum is debating the correct long-term temperatures for fancy goldfish. What do you think? Paul Green of the Ranchu Brotherhood and the Goldfish Society of Great Britain gives his opinion.

The answer depends on whether you want to breed your goldfish and if keeping them indoors or out. Assuming you are going to breed them, you will need to replicate seasonal changes.

In the UK, goldfish normally spawn in the spring as water temperatures approach 20°C/68°F and the fish are fully reconditioned from hibernation.

You can help by not allowing them to cool too low over winter and then slowly raising the temperature earlier in the year. In warmer countries, like Singapore, the opposite applies as average temperatures are much higher. In fact they need to cool their goldfish to breed them!

This demonstrates that goldfish will tolerate wide ranges in temperature, but any changes, up or down, should be gradual. So, what is the ideal temperature if you’re not about to breed them?

Around 22-24°C/72-75°F will promote good growth rates without stress, although as temperatures rise there is less dissolved oxygen available to your goldfish. Ensure an additional air source at all times.

Less showy goldfish varieties will cope from almost zero to 30°C/32-86°F as long as you provide the correct environment, like appropriate stocking rates.

 In my fish house water temperatures have reached 32°C/90°F and the equipment overheated, not the Ranchu. However, some fancy goldfish are not as hardy as some less showy relatives and stability is the name of the game, so avoid placing tanks near radiators or in direct sunlight.

If keeping fancy goldfish outside you will have far less control over temperatures but, in my experience, this has no adverse effects. In fact there are some benefits, in colour for example, and growth rates are good.  

This item was first published in the October 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.