Why Is My Piranha Not Eating? {Top 9 Reasons Explained}

Are you having trouble getting your piranha to eat? How long can your piranha fast until the stress, malnourishment and fasting becomes fatal? In this article, we’ll discuss the topic of why your piranha is not eating.

Why Is My Piranha Not Eating? Stress associated with insufficient space, cooler temperatures, loneliness, adjustment to a new tank, choice of food, poor water conditions or possible internal parasites could affect a piranha’s lack of appetite. 

Why Is My Piranha Refusing Food?

There are so many factors at play when your aquatic life refuses to eat. Let’s focus on your piranha and dive into the following 9 possibilities:

  1. Adjustment to an unnatural environment 
  2. Loneliness
  3. Tank is too small
  4. Cool temperatures
  5. Not enough water flow or hiding spaces
  6. Parasites
  7. Bullying
  8. Choice of food
  9. Poor water conditions

1. Unnatural Environments

Some aquatic life takes to life in captivity better than piranhas do. That isn’t to say it isn’t possible to keep piranhas and help them thrive in your aquarium, but it could take time.

They may initially refuse food. It will take time, but your piranha can go many days or weeks without eating. Be patient with their adjustment process, but continue to read on for more support to assist your piranha.

2. Loneliness

Piranhas enjoy life in groups. They are schooling fish and may end up refusing food from the stress of being alone. Add as many piranhas as you can under the tank space you have.

3. Tank Is Too Small

One piranha in a 20-30 gallon tank is best, but keeping them in groups is much better for them to thrive. Increase your piranha population, but also increase the tank size accordingly. 5 or more piranhas would keep them schooling, active and eating together during mealtimes. You may need a tank over 100 gallons.

4. Cool Temperatures

The cooler it gets, the slower the metabolism of your piranha. 75° and 80° F is ideal, but piranhas are used to drops in temperatures and pH in the wild. Raise the temperature to the higher end of this range to increase activity and appetite.

5. Water Flow And Hiding Spaces

The added water flow from a powerhead or air stones could help to aerate the tank. The extra flow of oxygen allows your piranha’s mood and appetite to pick up slightly. Also the hiding spaces from decorations and planted areas give comfort to help adjust to this new environment.

6. Parasites

Unfortunately, illnesses strikes when we least expect it. We hope your piranha is not ill, but internal parasites may surely reek havoc inside its guts and cause it to stop eating.

Check your piranha’s fecal matter for more information. Long stringy and white feces could spell the need for medication or a vet’s advice.

7. Bullying

Not all piranhas are created equal. Although they like to be in groups, some of them may not get a fair chance to eat or occupy the same spaces as more dominant members of the school.

If your piranha is getting picked on by its own species or other tankmates, the stress from it may cause a refusal of food. Remove aggressors or add dividers during feeding time.

8. Choice of Food

There is a common tendency to feed piranhas feeder fish or live food only. The truth is that you can train your piranhas to accept a wide variety of vegetables, frozen, dried food or pellets.

Also, if you are trying to feed your piranha a dead piece of meat, use tongs and mimic swimming patterns to get your piranha’s attention and entice it to chase after it for a deadly bite.

9. Poor Water Conditions

Half eaten food, fish guts and heads floating around are leftovers that will surely pollute your water quality. Ammonia will spike and it may leave your piranha stressed to the point where it won’t eat anymore. Reduce feeder fish, perform more water changes and check your water for these optimal levels:

  • pH: 6.5-7.8
  • Alkalinity: 50 ppm to 140 ppm
  • Nitrates: less than 5-10 ppm
  • Ammonia and Nitrites: 0 ppm
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What Should I Feed My Piranha?

Let’s start with what you shouldn’t or don’t need to feed your piranha. Goldfish may stunt the growth of your piranha and shorten their lifespan. They are also more expensive than other feeder fish.

Too many live feeder fish also creates stress when your piranha isn’t interested in actively chasing them around. The leftovers also spike ammonia levels. Here is a list of foods that piranhas enjoy:

  • shrimp (live, frozen, dried and pellet form)
  • frozen or fresh pieces of fish (salmon, tilapia)
  • chicken
  • bloodworms
  • omnivore flakes, granules pellets

A healthy tip for a piranha who is refusing food is to drip or soak the food in liquid garlic. The smell is potent and may attract your piranha to attack it. Garlic also helps to prevent parasites and boost their immune systems.

How Long Can a Piranha Go Without Eating?

A piranha in your aquarium may not seem to eat for weeks at a time. You may not notice it taking a few nibbles of algae or other detritus. Piranhas in the wild have adapted to going through long periods without eating.

Studies indicate they can fast anywhere between 2-3 months, but this is not the case in captivity. The length of time your piranha can go without eating depends on its size, species and age.

Anywhere between 7-14  days in your tank is considered an average amount of time that a piranha can fast without any adverse health effects.

How Do Piranha’s Eat?

We may have a picture in our minds of piranhas attacking their meal with ferocity, but this is not generally the case. Sure, they are ferocious and deadly, but they are also docile and opportunistic scavengers instead of taking on the role of predator.

Piranhas in the wild eat fallen fruits, seeds and nibble on plants and algae. They also eat crustaceans, amphibians and worms.

They are more interested in small healthy fish than a dying or sick one. If they discover a dead carcass of a larger animal in their native water, they may feast on it as well.

How Often Do You Feed A Piranha?

Once a day is fine for adult piranhas in your tank. Try to attach the food to tongs and make it look like it’s swimming around near the mouth of your piranha. See if this gets its attention.

Juvenile piranhas should be feed up to 2-4 times a day. Try to pick up any leftovers to keep your tank clean of ammonia spikes. Piranhas are messy eaters and can eat about 2.5 grams of food per day on average.


We hope your piranha resumes eating soon. Please take some of our suggestions into account to prevent any frustration or stress from seeing your piranha refusing food. Be patient for the adjustment period to take place and know that your piranha can fast for quite some time.


Thanks for visiting HelpUsFish.com and see you again soon for another piranha article that may interest you!

Brian Arial

Brian Arial has kept fish for leisure and worked with fish stores for most of his life. He enjoys writing and caring for aquariums and ponds.