Goldfish Temperature Shock – Symptoms & Treatment

Disclosure: I may earn a commission when you purchase through my affiliate links. As an Amazon Associate I earn from qualifying purchases. – read more

Goldfish are already notorious tank fish, famous for their graceful presence, color and pattern diversity, and hardy nature. They are great for both single-species and community tanks due to their ability to get along with most peaceful fish of similar size.

That being said, goldfish are prone to a variety of health issues, mostly related to water conditions, diet, and temperature.

Today we will discuss the latter, focusing on temperature fluctuations and how these can hurt your goldfish fast.

Can goldfish experience temperature shock, what are the effects, and in what conditions can the issue occur? Let’s see!

What is the Ideal Temperature for Goldfish?

A simple search on the internet will inform you that the ideal temperature for goldfish rests around 65-72 °F.

These are subtropical temperatures qualifying the goldfish as a cold-water fish. But this is a piece of unpolished information that generalizes aspects best understood via a more detailed look.

Here’s what I mean by that. Goldfish are generally divided into 2 primary categories with critical differences separating them in terms of adaptability and biological traits:

  1. Fancy goldfishFancy goldfish are the result of selective breeding, resulting in a variety of species like fantail, veiltail, telescope goldfish, bubble eye, ryukin, oranda, etc. All these fish showcase astounding features but also come with several implicit weaknesses. One of them is the increased vulnerability to temperature fluctuations, making fancy goldfish only suitable for indoor tanks. Fancy goldfish are also more sensitive to poor water conditions, which is why they require more frequent cleaning and tank maintenance.
  2. Slim-bodied goldfish – These goldfish are genetically closer to wild goldfish, which automatically means they are hardier and more adaptable than their fancy counterparts. They are more suitable for outdoor ponds since they can withstand lower temperatures and can even overwinter, lowering their metabolism as their environmental temperature drops. You can easily distinguish them from fancy goldfish via their slimmer and fitter bodies. Some options available include comet goldfish, waking, jikin, shubunkin, and others.

Both these variations prefer similar temperatures, between 65 and 72 F, but only the slim-bodied goldfish can withstand significant temperature variations with minimal downsides.

Fancy goldfish aren’t equipped to face drastic shifts in temperatures, with even variations of 2 degrees causing visible discomfort.

The conclusion is simple. If you wish to keep your goldfish in an outdoor pond, eliminate the fancy goldfish from the list.

Symptoms of Temperature Shock in Goldfish

Temperature shock is common in goldfish, especially during water changes when people disregard the importance of preventing abrupt temperature variations.

Even small variations of 2-3 degrees in water temperature can cause visible symptoms of temperature shock.

The signs of temperature shock will differ depending on where the value:

Cold Temperature Shock:

  • Visible lethargy – The cold water will force the fish to remain motionless in an attempt to conserve energy. Goldfish are cold-blooded creatures, and they depend on their environmental temperature to remain energetic and active. If the environmental temperature drops too low, the fish will conserve its energy and move less, appearing to be lethargic.
  • Resting on the substrate – Don’t mistake this for normal resting behavior since goldfish are occasionally known to rest on the substrate. The problem occurs when the goldfish remains near the tank’s bottom for long periods of time, especially after a water change. This behavior could signal some discomfort, usually relating to colder-than-usual waters.
  • Coma – This is already a sign that the situation is as worse as it can get. The goldfish may flip belly-up and display minimal-to-no activity, causing many to consider it dead. At this point, you should immediately heat up the water. If your goldfish hasn’t died, the chances of recovery are quite high. Fortunately, this doesn’t happen that often unless the temperature drops too low too fast, causing severe shock.

Hot Temperature Shock:

  • Rapid breathing – This happens because the hotter the water is, the lower the oxygen levels present. Your goldfish will immediately notice the change and will struggle to breathe as a result. They will display rapid gill movements, trying to pass on more water through them. They will also open and close their mouths more rapidly for the same reasons.
  • Erratic or overtly active swimming – Goldfish aren’t used to hot waters, so such an environment will immediately stress them out. They will display bursts of energy that they will spend erratically throughout the tank. You may see your goldfish swimming aimlessly all over their habitat, showcasing unusual levels of energy.
  • Signs of exhaustion – This happens when the goldfish remains too active for prolonged periods of time. The fish will exhaust itself and begin to appear lethargic, laying at the bottom of the tank.

Fortunately, goldfish are unlikely to experience temperature shock under normal conditions. After all, these are cold-water fish, so room temperature is perfect for them.

Most cases triggering temperature shock involve improper water changes, which may cause sudden temperature fluctuations that could take the goldfish by surprise.

How to Save a Goldfish from Temperature Shock?

The keyword here is speed. The faster you identify and address the problem, the higher the chances for your goldfish to recover in full.

Since most instances of temperature shock occur during water changes, here’s what you can do to save your goldfish’s life:

  • Monitor the goldfish during and after the procedure – This will allow you to identify any drastic changes in your fish’s behavior.
  • Have treatment tank ready – You should always prepare a bowl or a treatment tank prior to any water change. Set the water parameters to ideal conditions, including temperature, and keep it close in case your fish displays symptoms of temperature shock. Placing the goldfish into the treatment tank immediately will allow it to stabilize and recover.
  • Stabilize the temperature in the main tank – If the problem is temperature, check the values and use the heater to stabilize the environment. You can then move the goldfish back into the main tank, as long as the fish seems stable and healthy.

You may not always require a treatment tank, especially if the symptoms of temperature shock aren’t severe, to begin with. But you absolutely need one if your fish showcases aggravated symptoms or fall into a coma.

Placing the goldfish into a stable environment will allow for a fast recovery, and stabilizing the main tank may take time.

How to Avoid Temperature Shock in Goldfish?

I would say there are 3 easy fixes when it comes to preventing temperature shock in goldfish:

  1. Know your goldfish strain – If you have fancy goldfish, don’t keep them outside. Keep them inside, preferably in rooms where the temperature doesn’t fluctuate too much.
  2. Invest in a heater – While goldfish typically don’t need a heater, having one never hurts. The heater allows you to monitor and adjust the tank’s temperature to prevent dangerous fluctuations that could trigger temperature shock. Especially in fancy goldfish.
  3. Perform safe water changes – Improper water changes are always the primary cause of temperature-related goldfish problems. I suggest monitoring and adjusting the water’s temperature whenever performing a water change, even if you don’t think it’s necessary. Like I said, even small temperature fluctuations could cause your goldfish health issues.


Temperature shock may be scary-sounding, but the issue is manageable if you know what you’re doing.

It all comes down to identifying the warning signs in time and assisting your goldfish fast to prevent more severe repercussions.

Your goldfish are hardy creatures and will recover with proper assistance.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
Leave a Comment

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