Can Oscars Live In Cold Water? How Long?

Nov 24, 2021

Can Oscars Live In Cold Water

Image Credits: Daniella Vereeken (Creative Commons license)

Oscars are hardy fish. But like everyone, they too have an Achilles heel. In their case, it’s the water temperature. In this blog, we will discuss can oscars live in cold water or not. I’ll also touch on what are the risks of exposing them to the wrong temperatures.

So, without further ado, let’s go! 

Can Oscars Live In Cold Water? 

No, oscars cannot live in cold water. They are tropical fish from the Amazonian river basin where the water’s warmer. Therefore, oscars are not accustomed to cold water. If exposed, their bodies will react negatively quickly, and it can even prove fatal. 

Oscars are ectothermic creatures, which means they have no control over their body temperature. Instead, they rely on the temperature of their surroundings to regulate their metabolism and produce energy. 

Thus, when it’s too cold, the fish will become less active, appetite will be suppressed, and immunity will weaken. 

What’s The Best Temperature For Oscar Fish?

The suitable temperature range for oscars is somewhere between 74-81°F (23-27°C). So, to give you a specific number, the ideal temperature would be somewhere around 77°F (25°C). 

What Temperature Is Too Cold For Oscars? 

Anything below 74°F (23°C) can be deemed too cold for oscars. But the lowest temperature they can survive in is 55°F (12°C). But they will definitely not survive in such cold temperatures for long. 

A hobbyist on a fish forum shared that when the temperature dropped to 60°F (15°C) due to power failure, his oscars began to swim in weird patterns and looked deluded. 

Luckily, the power came back soon, and all of his fish successfully made it out alive. 

What Temperature Is Too Hot For Oscars?

Anything above 81°F (27°C) can be considered too hot for oscars. If the temperature goes higher than this, they might not show an immediate reaction, but they will eventually suffocate from lack of oxygen. 

Hot water temperature has one more disadvantage. It will demolish the good bacteria colony, leading to an ammonia spike in the tank, which will naturally harm your fish. 

For good bacteria, the optimum temperature range is somewhere between 65-85°F (18-29°C). So, anything hotter than that will kill them. 

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What Happens If The Temperature Is Too Cold For Oscars?

For tropical fish like oscars, exposure to lower temperatures can invite a plethora of complications. First, the fish’s metabolism will slow down drastically, making it passive. The fish will also get stressed. Over time, your oscar’s immunity will be compromised, and the fish will succumb to secondary illnesses. 

Fish Becomes Sluggish 

When the mercury drops, the fish’s metabolism will also naturally decline. As a result, your oscar’s ability to convert food into energy will decrease. And eventually, the fish will become tired and worn down. 

Your fish may then retreat to a quiet corner in the tank or lay motionlessly at the bottom. 

Fish Becomes Stressed 

Your oscar can be fit as a fiddle and still react negatively to even the slightest change in the environment. Like all fish, oscars don’t cope too well with changes in the water parameters. 

So, if the temperature drops suddenly, they will naturally get stressed. As a result, the fish will produce a stress hormone called cortisol in excess, which can suppress appetite and slow down metabolism. 

Some signs of stress in oscars are:

  • Frequently hiding 
  • Laying quietly at the bottom 
  • Swimming erratically 
  • Darting across the tank 
  • Heavy breathing 
  • Loss of appetite

Immune System Will Weaken 

In fish, the stress level is directly linked to immunity. So if your oscar is stressed due to a sudden drop in temperature, it’s only a matter of time before the fish’s immune system weakens – making it susceptible to an array of diseases. 

Fish Becomes Prone To Disease And Infections 

Lower metabolism, stress, and weakened immunity – you know what comes next – diseases! At any given time, whether you like it or not, tanks are infested with pathogens waiting for the right opportunity. 

They can’t do much harm to a healthy and happy fish, but once your fish’s immune guard is down, they’ll quickly make their way into its body. 

For example, a sudden drop in temperature is often associated with parasitic outbreaks like ick. 

What Happens If The Water Is Too Hot For Oscars?

If the water is too hot for oscars, their metabolism and breathing rate will speed up in unnatural ways. As a result, they will need more oxygen. However, the problem is that warm water holds less oxygen. Thus, they will slowly but painfully suffocate to death. 

Fish Becomes Hyperactive 

When the water is warmer than usual, the fish will become more active and eat more than usual. And this is necessarily not a good thing. A hyperactive fish is not amusing. 

Since fish are more active, they will need more food for more energy. And overconsumption can lead to obesity and other health complications. 

This is just one example of how hot water is equally bad for oscars as cold water, if not more. 

Fish Will Suffocate 

Warm water holds less oxygen. But since fish are more active in warm water, they require more oxygen. And so, your oscar will gradually suffocate. 

The fish will resort to heavy breathing first to intake as much oxygen as possible. Then it will resort to the tank’s bottom, where the water is relatively cooler and comparatively more oxygenated. 

And lack of oxygen isn’t the only way your fish will suffocate. 

Good bacteria that maintain the tank’s ecosystem start to die at higher temperatures, leading to dangerous nitrite and ammonia spikes. 

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How To Increase Aquarium’s Water Temperature During Power Cuts? 

People kept aquariums long before electricity was invented. So, there are a couple of ways to keep the tank heated even during power cuts. But remember, irrespective of what method you use, the process should be gradual. A sudden rise in temperatures can shock the fish and kill it. 

Here are a couple of things you can do:

  • Put the lid on the tank to retain the existing heat.
  • Keep the room warm. 
  • Perform partial water change with warm water.
  • Fill a plastic container with warm water and place it in the water.

How To Lower Aquarium’s Water Temperature Gradually?

A sudden drop in temperature is more dangerous for fish than warm water. Aim for only about 2°F or 1°C temperature drop every 8 to 10 hours. For this, you need to take note of the tank’s temperature right from the time the heatwave starts. 

Here are a couple of things you can do:

  • Turn off the aquarium lights.
  • Remove the tank from place that receives direct sunlight or warmth from heating unit. 
  • Remove the tank’s lid.
  • Place a fan in a position from where it can directly blow across the water.
  • Float ice bags in the tank.

How Oscars Adapt To Temperature Changes In Wild?

In the wild, oscars primarily live in South America, throughout the Amazon and Orinoco rivers and their tributaries. And naturally, the temperature in these rivers isn’t constant. As a matter of fact, they fluctuate pretty often. 

Some days the sun is scorching, while other days are cloudy. And sometimes, it rains, causing sudden temperature drops. So, how do oscars adapt to constantly changing temperatures in the wild?

First, they can quickly move from a cold area to a warmer and favorable spot if they don’t like the temperature. Second, although it may appear abrupt, these changes occur very gradually in the wild because of the colossal volumes of the water involved. As a result, the fish has a considerable amount of time to adapt and move. 

How Oscars Adapt To Temperature Changes In An Aquarium?

When it comes to sudden temperature changes in an aquarium, ‘suffer’ would be a more fitting choice of word than ‘adapt’ because enclosed within the 4 walls of your tank, your fish cannot escape. 

In the wild, the water temperature varies slightly or drastically in different microhabitats. However, the temperature is uniform throughout the aquarium. Therefore, your oscar cannot really move from a suffocating spot to a more comfortable one. 

On top of that, temperature changes in aquarium happen a lot in a tank, giving your fish no time at all to adapt its body to sudden change. 

How Long Can Oscars Live Without A Heater?

If the temperature falls within the 74-81°F (23-27°C) range, even without a heater, your oscar fish will go on to live for weeks. However, if the fish is consistently exposed to temperatures below 60°F (15°C), the fish can succumb to cold within a few days. 

Remember, oscars are tropical fish. Their body isn’t wired to handle cold too well – they thrive the best in slightly warm water. 

Here’s a quick look at the heater size chart below. 

Find your tank’s size in the column on the left-hand side and move right to find the number of degrees the tank needs to be heated.

Tank SizeHeat Increase by 5°C Increase by 9°FHeat Increase by 10°C Increase by 18°FHeat Increase by 15°C Increase by 27°F
5 Gallon/20 Litre25 watts50 watts75 watts
10 Gallon/40 Litre50 watts75 watts75 watts
20 Gallon/75 Litre50 watts75 watts150 watts
25 Gallon/100 Litre75 watts100 watts200 watts
40 Gallon/150 Litre100 watts150 watts300 watts
50 Gallon/200 Litre150 watts200 watts400 watts
55 Gallon/250 Litre165 watts275 watts440 watts
60 Gallon/272 Litre180 watts300 watts480 watts
65 Gallon/295 Litre200 watts250 watts500 watts
75 Gallon/300 Litre250 watts300 watts600 watts
90 Gallon/340 Litre270 watts450 watts720 watts
125 Gallon/473 Litre375 watts625 watts1000 watts
150 Gallon/567 Litre450 watts750 watts1200 watts

10 Tips To Maintain Right And Stable Temperature For Your Oscars

Credits: Justin Bradley (Creative Commons license)

Heating an aquarium is pretty straightforward – at least on paper. However, there’s no room for errors. One small mistake, and you can end up electrocuting the fish. 

Here are five tips on how to maintain the temperature in an oscar tank 

  • Don’t place your tank near windows, exterior doorways, heating or cooling units, and fireplaces. 

  • Don’t skimp when buying a heater. Choose quality over price. 

  • Select a heater with a capacity that’s designed for your tank’s size. Large tanks often need more than one heater. 

  • Ensure there is enough circulation around the heater for even heat distribution. (This extends the heater’s lifespan.)

  • Install a reliable and accurate thermometer and inspect it routinely to ensure the heater maintains the right temperature. 

  • While changing waters, match the temperature of replacement water to your tank’s water as much as possible. 

  • If possible, position the heater near the water outflow from the filter. This way, the moving water will disperse heated water throughout the tank. 

  • Don’t ever forget to unplug the heater when you are draining the tank. 

  • The heater tube should match the height of your tank. 

  • If your tank needs two heaters, place them at the opposite ends of the tank to ensure even heating. 

Final Words: Can Oscars Live In Cold Water?

Cutting to the chase – no, oscars cannot live in cold water. Why? They’re tropical fish. Centuries of evolution has wired them to thrive in warm temperatures. 

If your oscar fish is consistently exposed to temperatures below 74-81°F (23-27°C), it will hurt your fish’s health. First, its metabolism will slow down and make it sluggish. 

Second, the fish’s immunity will be compromised, and it will be prone to a host of diseases. For instance, ich outbreak is often linked with lower temperatures. 

However, hot temperatures can be just as bad for your oscar, too. The fish will use up all of its energy quickly and slowly suffocate due to lack of oxygen. 

So, you should always keep an eye out to maintain the right temperatures for your oscar. But remember, achieving stable temperatures is more important than fixating on one magic number. 

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rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.