Are Glofish Tetras Aggressive? {Do They Kill Other Fish?}

Glofish seem peaceful and harmlessly beautiful, but are glofish tetras aggressive?

What will they do to each other or other fish?

In this article, we’ll find out if glofish are aggressive and what we can do about it.

Are Glofish Tetras Aggressive?

Glofish tend to be peaceful schooling fish.

They could aggressive when the tank is overcrowded, during the mating process, territorial disputes or through fear and loneliness.

Please make sure to keep them in groups of four or more. 

Will Glofish Fight?

Glofish do not tend to fight, but they have the energy to chase and fin nip when feeling threatened. Common reasons for fighting include:

  • tank is too small
  • overcrowding
  • protecting territory
  • mating
  • fear 
  • loneliness
  • food

Give your glofish enough space and allow for them to school together in groups of four or more. Do not add too many aggressive fish in the same tank if it’s less than 20 gallons. Males will chase each other for the right to mate.

Fearful glofish are usually lonely and demand more glofish company. They will adjust to your tank if they have strength in numbers. Feeding times may influence some aggression, but as long as they aren’t harming each other, it will be tolerable.

Why Are My Glofish Scared?

You may have 2-4 glofish in your tank, but that might not be enough for them to feel comfortable. This number could be too low to be considered a school. Your glofish may not feel safe. Once the fear sets in, they will feel vulnerable in your tank.

If there are tankmates swimming near them, they may stick up for themselves instead of retreating. The instinct to defend themselves and their territory becomes more prevalent.

Here’s how to make them less fearful:

  • more glofish
  • increase hiding spaces
  • more plants 
  • add decorations
  • use dividers 
  • get a larger tank

Give them space and consider using a tank divider especially during feeding times. Your best bet is to increase their numbers to give your glofish more security.

The hiding places will give them options for a timeout when any potentially hostile situations call for it.

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Do Glofish Fight Over Food?

Smaller species of fish will fight or food against larger counterparts because there’s a genuine fear that they will starve if they don’t. Your glofish may end up being the smaller tankmates will team up to make sure they get their fair share of food.

This is a good time to add a divider in the tank when feeding your glofish. It may calm them down and protect their share of the food without forcing them to do it by themselves.

Are Male Glofish More Aggressive?

Male glofish will fight for the chance to mate with any of the females in the tank. They could end up fighting to the death if you haven’t stocked more females to males. Females are slightly larger and less aggressive.

If a female likes to swim in one area, the male will fight to protect that space for her. He will then get the right to mate with her. Stock a 2:1 ratio of females to males at the very least to prevent this type of aggression.

What Happens When Glofish Are Aggressive?

It’s important to note that glofish are not very aggressive. They are peaceful and we can do our best to keep the tank tranquil with ideal water conditions and temperatures. Plenty of room will be the best trick to keeping your glofish relaxed and happy.

The physical signs of aggression will start be become noticeable if you see:

  • missing scales
  • split fins
  • chasing
  • fin nipping
  • separate territories
  • excessive hiding 
  • refusal of food

Once again, ensure that the tank conditions are at the best you can possibly provide in terms of size and healthy parameters to prevent these types of stress from occurring.

Do Glofish Nip Fins?

Glofish may nip fins out of aggression or during the mating process. A male could nip at a female to indicate his desire to mate without it being harmful. Female glofish are known to nip fins to protect their eggs or fry.

Noticing split fins is a clear sign that your glofish were in a fight. They went a little too far this time because of a territorial dispute, a fight for food or the chance to mate.

How Can I Prevent Glofish Aggression?

If you cannot afford to buy a larger tank or if your space doesn’t allow for it, you can resort to changing things up in the tank. The decorations, plants, substrate and anything else that you’ve done to create an healthy environment for your marine life can be altered a bit.

The key is to confuse the aggressive fish who were spending too much time and effort defending their territory. Once you change the settings, the confusion sets in and things tend to reset. This is when everyone in the tank tries to establish themselves and get comfortable in a better way if previous conditions were getting too intense.

Continue to test the water and make sure the following parameters are set:

  • pH level of 6.2
  • 3-6dGH hardness
  • water temperature 74-84°F


Glofish are not very aggressive. They are active and comfortable in a school of four or more. Increase their numbers, but stock more females than males to prevent aggression from mating behavior. Different situations lead to different outcomes.

Your experience level continues to improve and your keen sense of awareness is allowing you to notice any aggression and your methods of alleviating them are getting sharper.

If you can get a larger tank or change up the environment a bit, you may be able to stop any chance of aggression in glofish who want to live peacefully in your aquarium.


We wish you and your glofish the best of luck and happier days ahead. Thank you for visiting and come back soon for another article on glofish!

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.