Generally, neon tetras are one of the most popular freshwater fish for your aquarium.  They are tiny, brightly colored, and take up very little space in your aquarium.  

They are not aggressive and seem to be able to get along with most other fish.  Suddenly they are fighting but not sure why.  Silly as this may sound, it could just be their manner in which they are swimming that makes them seem as if they are fighting amongst themselves.  There are times that they do fight and it is an act of aggression.

Neon Tetras Swimming Manner

Neon tetras love to swim in schools and have their own swimming pattern.  It seems to be a normal thing for them to be swimming in their pattern as a school and then they start to fight with each other.  It could be that they are irritated or maybe one of the other fish in the school bumped against them.  They just lose their temper and start to fight.  

This is why you mustn’t overstock your aquarium with neon tetras fish.  For a 10 gallon aquarium, you should not have more than seven or eight neon tetras fish.  There are some very active neon tetras and these are the ones that are causing the trouble.  If their behavior remains strange after twenty-four hours, you should talk to a professional about the behavior.

When there is a sudden change in their behavior, it could be an indicator of stress or disease.  If they change their swimming pattern monitor the parameters of the water.  There could be something stressing or irritating them and causing them to attack each other. 

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You also need to be alert if the neon tetras are not exploring around the aquarium.  It could be that they are feeling threatened by something or another fish or they are sick.  Try to feed them and see if their swimming pattern returns to normal.  If it does not, then you need to find out why.

tetra in aquarium

Nipping at Fins

It is a known fact that neon tetras are fin nippers.  Most fish will nip at other fish’s fins if they are stressed and for some it is a normal behavior.  You will not have to worry about it unless it becomes extreme.  Neon tetras love to chase each other or other fish without showing aggression or displaying any intention of attacking.  This fish is very playful and can be a handful for beginners who have never had neon tetras.  Some think that when they see fin nipping that the two fish are attacking each other and are fighting.

Here are some reasons they might be nipping the fins

  • Introduction of new Neon Tetras:  When a new neon tetra is introduced to the tank, the other neon tetras will chase it and nip at its fins.  This is because this new fish is a stranger to them.  This could last a while until they get used to each other and start to get along in the same aquarium.
  • Dominance:  Some neon tetra wants to be the dominant one or they are the dominant one and want to show the new neon tetra where they fall in the pecking order, so to speak.  It could be that the dominant one just wants to pick on the new neon tetra
  • Territorial:  Nipping at the fin is showing that the neon tetra has its own territory and does not want the new fish in it.
  • Protection:  It could be a way of defense and protection against any threats that the neon tetra might feel.
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Fighting or Playing

Neon tetras are known to be playful, tricky creatures so when you see them chasing each other continuously you wonder if they are fighting or playing.  They could be fighting if you have too many neon tetras in an aquarium that is not big enough for them.  The reason they would be fighting then is that they do not have enough room to freely move.  They also do not have enough room to practice their swimming manners in a group.  

blue neon tetra

Fighting or Mating

When neon tetras are practicing their mating rituals, it can look like they are fighting.  When it is mating season, the male neon tetras will be fighting with each other in order to choose the female they want to mate with.  To be sure that they are not fighting, put a male and female neon tetra in a different aquarium that has the right conditions for mating, and then spawning.  If the male starts to swim in a square pattern and is acting odd, then the mating is about to state and the eggs will soon be fertilized by the male.  

Neon Tetras Fighting

Neon tetras do not get along with a larger fish because the larger fish could bully them continuously, or eat them.  If this is happening, put the neon tetras into their own separate aquarium.  Fighting can also be a way of expressing aggression.  They are good at detecting the slightest change in their habitat conditions.  If their habitat has changed in any way, it could affect their behavior.  They may get stressed, refuse to eat or even start to fight.  This could lead to their death if it is not taken care of.

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Attacked and Bullied—What Happens

If your neon tetra starts to lose their color or no longer swims with the school, it could be bullied.  In this case, you need to find out which one is bullying the neon tetra and remove it from the aquarium.


  • To keep the neon tetras from fighting or fin nipping, make sure that you have a large enough aquarium for them to practice their swimming manner and to move freely about.
  • If they are fighting, make sure that ammonia levels in the water are correct, check to make sure that the temperature is right, and the water parameters are correct on a regular basis. r
  • Disease can also be the cause of why they are fighting.
  • The main factor in why they may be fighting is stress.
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Hi! I'm Anna and I´m a certified cynologist (KAU, ACW). Expert, blue cross volunteer, owner of Chinese crested kennel "Salvador Dali" and breedless friend called Fenya. "I can't imagine my life without dogs and I totally support the idea #AdoptDontShop".