Are my Guppies Stressed? What is Fish Stress?


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Just like with humans, stress is a serious problem with fish too. Often stress is the main inducer of many guppy illnesses.

But what is fish stress? How to know if your guppy fish are stressed and sick? What to do if you see signs of stress or strange behavior? Will stress make your guppies sick? Will stress cause death? I will give you detailed answers to these questions in this article.

In short, stress in fish including guppy fish, is caused when fish is kept in unsuitable conditions. Although guppies are a very hardy and highly adaptable fish, there are still many cases when they could not be comfortable with their environment, in this case with the aquarium they are kept in.

Stress reduces the fish ability to fight off diseases that are not fatal for the fish. Stress is also reducing the fish ability to heal itself in case of injuries.

Stress will also reduce guppy fish appetite and discourage breeding. Overall stress will reduce the lifespan of your guppies and will eventually result in death.

Here are the top factors that will cause guppy fish stress:

  • low water temperature
  • small or overcrowded tank
  • aggressive tank mates
  • poor water condition

Stress can also be caused by transportation or handling. If you are moving your guppies to new environment or shipping them, it is a good idea to use the Seachem StressGuard, which you can buy from Amazon. This product reduces stress and ammonia toxicity.

In the following I will explain each stress factor in detail. Please keep on reading.

Low Water Temperature

Guppies are tropical fish, so they can’t live in cold water. Guppies can live in water with temperatures between 65-85 °F (18-30 °C), but if you want to keep and raise healthy fish, I recommend keeping a stable temperature. I found that guppies will thrive in water with temperatures between 75-78 °F (24-26 °C).

To keep a stable water temperature in your guppy fish tank, I recommend getting a heater. This is the best way to avoid any fluctuation.

Small or Overcrowded Tank

For guppy fry I recommend 0.5-1 US gallons (2-4 liters) of water volume per fish. For adult guppies, I use the 1 inch / gallon rule to calculate the maximum number of fish per fish tank.

Female guppies can reach up to 1.5 inches (in rare cases even up to 2 inches), while male guppies only up to 1.2 inches. Considering these numbers and the 1 inch / gallon rule, you can add 6-7 guppies to a 10 gallons aquarium.

You don’t need to follow this rule so strictly. Your guppy fish might be fine if you add one guppy per gallon, but I don’t recommend going above this number.

In an overcrowded tank, some fish will become very territorial and pretty much will fight other fish for that territory. This can be a huge stress factor.

Small tanks are also a common stress factor for fish. You can keep guppies in smaller tanks, but to ensure they stay healthy and have enough room, I recommend at least a 10 gallon (40 liter) aquarium.

Aggressive Tank Mates

While guppies are peaceful fish, they won’t fight back if a more aggressive fish will approach them. Guppies will try to run away or hide from the aggressive tank mates. This is very stressful for the fish, so you should avoid mixing guppies with more aggressive fish.

I don’t recommend keeping guppies with angelfish, barbs or other fish, which is big enough that can eat them. In some rare cases guppies can live together with bigger fish.

I’ve seen fish tanks, where guppies were kept together with a freshwater puffer fish. This setup can work, because the puffer will not eat the guppies. Puffers eat snails, crabs and clams, and they are not interested in guppies.

Here is a great video that shows how puffer fish and guppies can live together:

Poor Water Conditions

Although guppies can take a wide range of water parameters, there are few things to consider when setting up a guppy fish tank.

Guppies are tropical fish, so they live in warmer waters. The ideal water temperature for them is between 75-78 °F (24-26 °C). They can go lower or above these temperature, but not for long. In colder water, below 74 °F (23 °C), the chances of guppies getting sick are higher. In warmer water, above 86 °F (30 °C), the level of oxygen stars falling.  Eventually oxygen is depleted and fish will die due to asphyxia.

So make sure, that you get the proper water temperature for your guppies. The best way to keep a stable temperature is to get an aquarium heater. If in the summer the water gets too warm, increase the surface agitation in the tank. Adding an air-stone or pointing the filter output to the surface of the water can help with increasing surface agitation.

Surface agitation will provide a greater oxygen exchange and will also help to cool the water through evaporation.

Ok, water temperature is one thing, but what about pH level?

I’ve written a detailed article about how water pH level will affect guppy fish. In short, the best is to keep your guppies in water with pH levels between 7 and 8 (you can use a test kit to measure water pH level – I recommend this on from Amazon). Usually, tap water is great for keeping guppies, so you don’t have to really bother to measure the pH level of your drinking water. It will be just fine for your fish, just use a water conditioner to remove chlorine, chloramine and heavy metals.

Ammonia, nitrites and nitrates are the waste products of your fish. There are different test kits, which are suitable for measuring the levels of these compounds.

Fish waste, decaying fish food, decaying fish body or decaying plant matter, will turn into ammonia, which is highly toxic, deadly for the fish. Beneficial bacteria will convert ammonia into nitrites, which is less toxic for the fish, but still deadly. Eventually, nitrites will be converted to nitrates, which is toxic to your fish only in higher quantities. This process is called the nitrogen cycle.

In a well- established tank, the cycle is instant, and no ammonia or nitrites are accumulated. Nitrates will accumulate overtime, which can be removed or lowered through weekly water changes.

So to recap: keep ammonia and nitrites at 0 ppm and nitrates less than 20 ppm. This way you can ensure that your guppies will be happy and not stressed.

Adding live plants to your aquarium can help reduce nitrates, because plants will consume this compound in order to grow.

Symptoms of Stress and Illness in Guppy Fish

Here are the most common signs and symptoms of stress and guppy fish diseases:

  • guppy fish loses its appetite and eventually stops eating
  • guppy fish will hide continuously or will sit on the bottom of the tank
  • stressed guppies will lose some of their color and will become pale
  • guppies may stay near the surface gasping for air
  • nicked fins or injuries on their body
  • cloudy or swollen eyes (this can be caused by bacteria or internal parasites)
  • female guppies will get extremely thin after giving birth (caused by stress during labor)


Stress is one of the main causes of guppy diseases. Finding the exact cause of stress and treating the illness accordingly with proper medication is a must if you are concerned about the health and life of your fish.

If you are using a medication, remember to turn off UV sterilizer and remove the active carbon from your filter, because these will neutralize the medication, having no effect on your fish.

Keep your guppies together with non-aggressive fish. Feed them a variety of high-quality food. Do your weekly water changes and maintain your fish tank regularly. Heat or cool the water as temperature requires. Enjoy your beautiful and healthy fish.

Updated: October 9, 2021
Questions & Answers
  1. Kadence Smith

    I have had a male guppy in my 10-gallon tank for a month or two now but all of a sudden he started hiding and I saw his tail was a little ripped. When I first got him he loved going around the tank and trying to breed with the females. I have 2 males and 3 females. There is no visual sign of sickness. Do you know what’s going on?

    1. avatar

      There could be many things why your male guppy is hiding, these are what I think might be happening:
      1. it is bullied by the other male (this is most likely to be the case, because of the ripped fin)
      2. has an internal parasite which does not have any visual sign just yet

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