Piranha Behavior

Most people have a misconception that the more piranhas in the tank the more aggressive they will be, this is not true, infact keeping too many piranha together only contributes to their skittishness. They do not fully trust one another, and being cramped in close quarters with each other only makes them more skittish and causes them to dart all around the tank, its what I call a "Paranioa chain-reaction." One piranha may swim to close too another and the piranha will be afraid of being nipped by the other, then darts away scaring another piranha causing a chain-reaction of the whole school to bash their heads into the tank walls trying to get away. This also leads to the misconception of piranhas being very skittish, they are just shy fish. I keep 2 red belly juveniles, that live in a 60gallon tank, they are not skittish at all, because they have alot of room between each other. The only time they get scared and hide is when I have my hands in the tank.

In general most piranhas are shy and not that aggressive, so do not buy any piranhas if you think they are vicous aggressive fish that can kill anything, because they are not. There are exepctions however, such as the Black Piranha (Serrasalmus Niger), White Piranha (Serrasalmus Rhombeus) Black Diamond Piranha (Serrasalmus Spilopleura) etc. I would NOT recommend these species to any beggining piranha keeper.

When you first buy your piranha and put them in their new tank, they may act very wild and bash into the tank, or even play dead, dont worry, this is normal for newly bought piranhas. This only lasts untill they get used to their new surroundings.

A piranha playing dead.

Frequently Asked Questions:

This is a list of questions asked most by beginners to the hobby the get answered countless times. The majority of these questions pertain to Nattereri or Red Belly Piranha which is what almost all beginners have.


  1. How many piranhas can I keep in a ___ gallon tank?    This is a rough list but here goes.         

    30 gallon tank One piranha
    55 gallon tank Three piranhas
    75-90 gallon tank Four to Five Piranhas
    125 gallon tank Five to Seven Piranhas
  2. My red belly lost its color at night is it O.K.?    Yes, piranhas tend to lose their color at night and when they are stressed, they will gain color when they are happy and when they are fighting.

  3. What is the proper tank temperature for piranhas?    Between 74 and 86 is O.K. with 78-82 degrees Fahrenheit being optimal temperature.

  4. My piranhas freak out when the tank light comes on what can I do?    You need to lessen the lighting which can be done in several ways. First way is to use car window tint to cover the glass panel in the lid to reduce light by whatever ratio of tint you get. The second is to wrap half of the light tube (fluorescent only!) with electrical tape with a candy cane pattern. The final method is to spread aluminum foil over the glass panel with various hole poked through it to allow rays of light through.

  5. What should I feed my piranha? A variety of food is best. For healthy fish stay away from feeders. Piranhas do well with beef heart, shrimp, krill, steak, chicken, smelt, nightcrawlers, squid, fish fillets, pork and other various frozen meats. Make sure the meats do not contain any preservatives because they will destroy your fish's digestive system.

  6. How fast do piranhas grow?    During adolescence piranhas grow around an inch per month until they reach around seven and a half inches after that it is usually around one to two inches per year.

  7. What sex is my piranha? Though it can be very hard to tell once you learn you fish's' character it can be possible. Read here Supernate's Piranha Sexing for more.

  8. What kind of piranhas can be kept together?    Pygocentrus specie piranhas can be kept in groups and Serrasalmus usually most be kept solitary

  9. How long do piranhas live?    Piranhas in captivity have lived more than twenty years, but ten to fifteen can be considered normal.

  10. What is the meanest piranha?    This question doesn't have and definite answer. However the Serrasalmus species have a high level of aggression and territoriality which make them meaner fish. The top three mean fish would be S. Rhombeus, S. Elongatus, and S.Brandtii in no specific order

  11. My piranhas are skittish, how long will they be this way?    Juvenile piranhas are this way for a reason, it is their only defense at small sizes in the wild. Red bellies are the most skittish of piranhas and will remain that way until the start reaching maturity which is around six to eight inches.

  12. My piranha is rubbing its sides in the tank, what is wrong?    Piranhas are like any other animal the scratch when they itch. However pay attention when this happens it can be a sign of several bad things. You water quality could be poor, the piranhas could be sick or have an infection, fungus  or parasite. So examine the fish and other fish of the tank if you see this behavior.

  13. My piranha lost a fin how long does it take to grow back?    Piranhas regrow fins very quickly for a good reason, think of how many times the lose them around other piranhas. Fins can be completely regrown within two weeks.

  14. My piranha lost an eye, or its lips will it grow back?    Eyes will never grow back and lips rarely do completely.

  15. My piranha suffered a body bite what should I do?    Separate the wounded fish with either a divider or a hospital tank and then treat it with one tsp. of aquarium salt/ 5 gallons of water and a tank temp of 82 degrees. This treatment solves most piranha ailments occurred.

  16. What pH should my water be? What hardness should my water be? What should be the ammonia, nitrite and nitrate readings  of my water be?    Check here Supernate's Tank Care

  17. What other fish can I put with my piranhas?    Though it isn't guaranteed success these fish fair best with piranhas. Black fish  that are fast do much better than other fish. Convicts and Plecostumous are the most successful that I have dealt with. Other possible tank mates are neons, tiger barbs, oscars, rainbow sharks and snails.

  18. How can I maximize the growth of my piranhas?    Several things can be done to maximize growth. First you can buy a powerhead which will create a strong current in the tank for the fish to swim against and exercise more. Feeding twice a day with high protein foods will also help. Keeping the tank temp close to 82 degrees is another important thing. Fish also grow much faster if their tank water is clean, so I recommend a weekly cleaning of at least 20%, I change about 30% weekly on my tank.

  19. My piranha has an infection on it or a bite how should I treat the piranha?    The safest treatment is to follow Clay's treatment which is Maracyn II on days 1,2,3,4,5,6
    Penicillin on days 1,3,5. Treat one tablet per 10g. Most other products out there will kill piranhas because they are highly sensitive to medications and other chemicals.

  20. My piranha lost its teeth what will happen now?    Piranhas shed their teeth a whole row at a time either top or bottom. The grow back quickly and sometimes you don't even see the teeth because the lips cover them.

  21. The Local Fish Store (lfs) has a piranha labeled ____ what kind of piranha is this?    Piranhas are frequently mislabeled in lfs. The best way to determine what specie the fish is, is to figure out what genus it is either Pygocentrus or Serrasalmus which is quite easy to do all you have to look at is the head and whether its concave or convex. Concave means  it is a Serrasalmus and convex means it is a Pygocentrus . Then follow that link to that Genus's page and try to match a picture with that fish and I have listed the most frequent aliases with each fish. If you are still un-clear try looking at the bottom of this page Click Here! If you have any further questions about identification you can

Understanding Your Piranhas:

   This section is designed to help you understand what your piranhas behaviors mean and to help you care for them better by recognizing these signs.


-When piranhas aim towards the gravel and tilt their tail upward it is a sign of aggression, in most cases they do this to keep somebody from coming into their zone.

-When piranhas grow very pale in appearance, it means that they are stressed for some reason or that the tank light has just come on so their colors haven't came out yet.

-When piranhas turn on to their side and rub the gravel, they are trying to itch themselves for one of several reasons that are usually due to poor water quality, infection or disease, and occasional they just need to scratch just like any other animal.

-When piranhas hold their mouth open and wag violently side to side it is a warning that they are ready to fight.

-When piranhas chomp their mouth repeatedly they are hungry and want you to feed them.

-When piranhas constantly circle an area they are showing that is their territory and others are not welcome, it can also be a sign of displeasure with what ever is going on in other parts of the tank.

-When piranhas colors get really intense it means that they are either really happy or very angry.

-When piranhas get really dark almost black it means that they are wanting to breed.

-When piranhas get side by side and wag their tails at each other they are fighting or breeding.

-When piranhas bite at each others' fins it is their warning that if the others action continues that they will be killed.

Disease & Treatment

These are the only diseases I have ever encountered while keeping piranhas. Remember, before treating your fish for any disease remove the carbon first. If you dont then the medication will be absorbed into the carbon. Always follow the instructions on the medication to be used.

"Ich"- Small white cysts on the fins and body of the fish. The fish will also try and scratch itself against rocks, gravel and other decor. This is a protozoan and can be treated with readily available medications from your local fish store.

"Fin and Tail Rot"- I have encountered this disease with my more delicate wimple piranha. This disease shows up as clouding on the edges of the fins, and progresses to severely frayed and even destroyed fins. This disease should be treated immediatly with a broad spectrum nontoxic antibiotic. This medication is also readily available at your local fish store.

If you properly care for your piranhas, diseases would rarely show up. Most diseases can easily be prevented from the start: When buying feeder fish for your piranha, select only feeders that are healthy looking and active, avoid lethargic feeders that look very sickly. Always quarantine new fish before introducing them to your main tank

Piranha's Healing Abilities:

    Piranhas possess an amazing ability to regenerate fins and heal from body bites. Typically a piranha can completely recover from a bite or wound in less than 3 weeks or faster. If you think about this ability it is a vital one. Piranhas live in a world where the weak are eaten and don't survive so they cannot afford to be injured long. And in the life style of living with other piranhas bites will most likely be frequent. What this all means is that through evolution piranhas have adapted to heal very fast so they can continue to survive. Below is a table of photos of my Cariba Pedro. Pedro is the king of the tank and barely even has a bite so this was a unique experience all together. He is normally the one beating everybody else up. The photos were taken 24 hours apart give or take 30 minutes. So the day by day progression is quite accurate example. Water parameters during this recovery: pH 6.4, Temp 80 F, water hardness 8ppm, ammonia and nitrites near zero. Nothing was added to the water and everything was kept on my normal routine of tank cleaning every other week, feeding every other day, and use of automatic water changer.



Day: Photos: Click to enlarge!
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Piranha Care

This is a basic chart for new piranha owners.


The safe range of temps are (74-84) with minimal fluctuations.

pH levels:

 Between (6.2-7.2) are safe as long as they are kept constant.

Ammonia levels:

0 - 0.25 parts per million are safe

Nitrate and Nitrite levels:

0 - 0.25 parts per million are safe

General Water Hardness:

3 - 8 parts per million is the ideal range however 3 - 15 will be okay

Food (diet):

Try to feed a mixed variety twice a day of Krill, Shrimp, Beefheart, Earthworms, Smelt, and Chicken. Live food should be avoided due to the HIGH RISKS of disease and parasites!

Lighting levels:

Keep light to a minimum as piranhas aren't adapted for bright light situations.

Size of tank:

About 20 gallons per fish, keeping more than 3 fish to minimize fighting.



Changing Water Parameters:

    In most cases its best not to try and change your water parameters. Fluctuations in most of the parameters stress your fish and sometimes harms them or in some cases it kills them (usually pH bounces and ammonia spikes). In my opinion the only safe way to alter pH is through 2 methods. I never use chemical additives for pH as they can and do cause deadly pH bounces. To lower pH add peat moss to your tank either in the filter or pre-treat the water. I put 1 cup of peat per 7 gallons of tank water in a nylon stocking and tie it shut, then place it in my filter and leave it in there. Peat will add a yellow-brown tint to the water and it also softens the water which is good for piranhas as well. You may need to use more or less peat depending on your tap water and your desired pH range. To raise pH I suggest using crushed coral, this also raises water hardness too though, I personally dont see any reasons why you would want to do either for a piranha tank unless your tap water has a really low pH which could indicate a problem in its own.




 Piranhas are native to the Amazon river region in South America. There is little water flow in the river which makes the water stagnant. Most piranhas have a high body so they can power their way through the slow water. Due to the lack of current dead decaying matter will remain in an area and rot raising the levels of toxins in minerals in the water. Due to the high amount of decay the Amazon has slightly acidic water. Piranhas do best in a pH range of 6.2-7.0.

      The water remains quite warm in the Amazon as well. Piranhas are a cold blooded creature and get their energy from the temperature of their environment or water temperature. Ideal range for the temperature in an aquarium is 76-82 degrees Fahrenheit. At higher temps piranhas will show higher amounts of aggression, if you experience high amounts of aggression lower the temperature gradually by 4 degrees. Its very important to make small changes in water properties or you could kill your fish.

      Ammonia ,nitrate and nitrite are results of decay from food and waste. Because of the nature of piranhas feeding behavior they are quite messy which can create a rapid rise in these levels so it is crucial to remove all uneaten food within a few hours. I check my levels for pH, ammonia, nitrate and nitrite once a week. I also clean the tank thoroughly with a gravel siphon and do a 30% water change every ten days or as needed sooner. When water is changed it must be treated prior to putting it into your tank. You need to have chlorine remover, pH adjustment kit, and make sure the temperature is close to that of your tank. 

    Here is a brief overview of where your fish originated from in South America.

Click to enlarge the map!


Piranha Species

Orinoco River P.Cariba, S.Altuvei, S.Eigenmanni, S.Irritans, S.Manueli, S.Rhombeus, S.Spilopleura
Amazon River P.Nattereri, S. Elongatus, S.Rhombeus, S.Spilopeura, 
Negro River P.Nattereri, S.Gouldingi,
Paraguay River P.Ternetzi, S.Spilopeura,
Parana River P.Nattereri, S.Spilopeura,
Sao Francisco River P.Piraya, S. Brandtii

    Now that we have covered water parameters for you fish it is important to discus the feeding of your piranhas. Piranhas in nature feed on fins of fish, whole fish, fruits, insects, and mammals. Piranhas generally hunt the weak and injured. Piranhas are attracted to blood and erratic splashing just like sharks. When feeding piranhas there are a few things to keep in mind. One, you need to provide a well balanced diet of a variety of foods that contain all the essential vitamins. Most people feed goldfish as the main food source to their piranha. This is not a good diet because goldfish are high in ammonia and provide small nutrients. Goldfish and other feeder fish in general cause or carry high amount of bacteria and diseases which can possibly kill your fish. Before feeding live animals they need to be quarantined for a few days to make sure there aren't any signs of sickness. A good diet for piranha would be slices of beef heart (high in protein), shrimp (preferable with the shell for more vitamins), cleaned earthworms, slices of frozen fish. All of these foods are available in local grocery stores and can be kept in the freezer to prevent spoiling. Simply cut the meat into small cubes freeze on a tray then put them into a storage bag. Thaw the food in a cup of warm water prior to feeding, this method is very simple and provides a good diet for your fish. Feeder fish can be given on occasion as a treat and will keep your fish from being lazy. While your fish are growing and maturing most they should be fed every twelve hours. Only feed them however much they can consume in about five minutes. After they reach a size of seven inches feeding is only necessary once daily.

    Keeping piranhas is illegal in several states because of the danger that piranhas can survive over the winter in that area and possibly form a large population and kill off all of the natural species of fish. Many people report catching a piranha, but in most cases is the look-a-like Pacu. This is a map of the legal status of piranhas.


    Most states have severe fines and possibly jail time if you are caught with illegal fish, yet they can be found in some fish stores.  

    Safety around piranhas is important. Piranhas are very skittish and the likelihood of you being injured is small yet, you need to respect the fish. Never put your hand in the tank near feeding time because your fish are accustomed to food entering the water during this time. They may mistake your hand for food. Never put any of your body with a open wound or healing in the tank because they are attracted to blood. When cleaning the tank be sure not to corner the fish as they will feel endangered and may attack to protect themselves. As your piranhas grow larger the danger increases dramatically. The fish become bold and strong enough to possible bite a finger off or cause other serious injuries. The most dangerous piranha is the one that is flopping on the floor. As they flop they continue to bite rapidly in fear. When moving piranhas with a net never put your hand under the net as piranhas bite through it and may fall out and bite you. You can insure your own safety by remembering one simple thing and using common sense "their teeth aren't a joke they are real and dangerous." 

    Setting up an aquarium for piranhas is simple. Provide good filtration, a good strong heater, low lighting and provide plenty of hiding areas for them. A good filter that is designed for a tank larger than your own would be ideal because of the amount of waste piranhas create. Piranhas are powerful and dart through the tank and could possibly break your heater so make sure it is strong. Plant your tank thoroughly and use rocks and driftwood that are aquariums safe to provide a natural habitat. This way your fish have room to get away from aggression from others. As a general rule of thumb you will need at least 20 gallons per piranha you plan to keep. They grow quite large and some species grow fast. As with all fish the larger the tank is the better off you will be. Larger tanks need less maintenance as well. Use very little light as well because the Amazon river is very dirty and visibility is very low. Piranhas don't get much light and their eyes have adapted to low lighting. If you use to bright of lighting your fish will hide in the shadows and will dart erratically when the lights are turned on. To provide a natural environment use rocks, driftwood pieces, and live plants like Amazon swords. Arrangements can be made quite dense. In the wild they basically live in a flooded forest for 4 months so they are used to and like lots of decorations. This is a good example of what a tank should look like.

    Piranha behavior in general is nothing like their myth. People think that piranhas are viscous killers. That is far from the truth. Piranha are very skittish  and stressful. You need to avoid stressing them at all costs. Tapping on the glass is a big element to their stress. Keep noise to a minimum around the tank. People often buy these fish looking for a thrill, but the fish often disappoint new owners. Piranhas aren't very active until feeding time. During this time you will see what their myth came from, but is the only time they act that way. Piranhas will often dart away from you in fear until they get used to you. Proper stocking levels must be used to lessen stress as well. The lower the stress the fish have the happier you will be with piranhas.



How to treat a sick or injured piranha:

    It is important to stay away from most store bought fish medications, piranha generally are very reactive to these medications and it can kill them easily. In most cases no treatment is needed for a piranha to recover. Piranhas can regenerate fins within 14 days usually. For body bites it is recommended to put the injured fish in a separate tank or hospital tank. A tank temperature of 84 degrees, adding 1 tsp of aquarium salt per 7 gallons of tank, and doing 20% water changes every other day is the best treatment. Try not to feed or stress the sick fish at all costs. However if infection does occur (looks like cotton) use the Clay Gamer medication below. All these products should be available at www.bigalsonline.com

Maracyn II on days 1 - 6
Penicillin on days 1,3,5

Treat one tablet per 10g.

Remove carbon from filters while medicating fish, it removes medication, and then put it back in once treatment is finished to remove the rest of the medication from the water. Make sure not to put the fish back with the others until it is completely healthy, piranhas can sense weakness and may attack the recovering fish. The only piranha I lost to cannibalism died from putting it back with the shoal too soon.


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