Keeping fish is relaxing, but things can quickly become stressful when fish start fighting inside the tank. Chasing, fin-nipping, biting, or one fish bullying another can lead to injuries, stress, or even death. Many beginners blame the fish, but most of the time, the real problem is the tank environment or wrong fish combinations.
In this simple guide, you’ll understand why fish fight and the easy steps to fix it safely.
1. Why Fish Fight in an Aquarium
They fight mainly for three reasons:
A. Territory
Some fish, like bettas, cichlids, and gouramis, naturally protect their space. If the tank is too small, they become aggressive.
B. Incompatible Tankmates
Peaceful fish and aggressive fish cannot live together. Some fish bully slow-moving or long-finned fish.
C. Bad environment or stress
Poor water quality, lack of hiding spots, or sudden changes can make fish behave aggressively.
Once you know the cause, it becomes pretty easy to fix.
2. Give Enough Space
One of the largest causes for fighting in fish is overcrowding.
When too many fish are in a small aquarium:
They struggle to make room.
Water becomes polluted quickly
Aggressive fishes become more aggressive.
Easy Fix
Increase the tank size, where possible
Follow the basic rule: 1 inch of fish = 1 gallon of water (not perfect but helpful)
Keep small fish that need schooling in schools or groups.
More space = less fights.
3. Add More Hiding Spots
Many beginners keep tanks with only open space. But fish feel safer when they have places to hide.
Add:
Live plants
Driftwood
Rocks
Earthen pots
Caves
Decorations
These hiding areas break the line of sight and stop dominant fish from constantly chasing others.
4. Rearrange the Aquarium
If one fish has already claimed territory, it will defend it aggressively.
Simple trick:
Rearrange the tank setup while cleaning.
Move plants, rocks, and decorations around.
This resets territory, so all fish start off clean.
It minimizes aggression almost immediately.
5. Avoid mixing wrong species.
Some fish are just naturally not compatible. For instance:
Betta males fight other long-finned males
Tiger barbs nip fins of slow fishes.
Cichlids fight for dominance.
Goldfish and tropical fish require different conditions.
Check before buying:
Temperament
Size
Water condition
Group behavior
Picking the proper tankmates prevents 90% of fighting.
6. House Schooling Fish in Correct Numbers
Some fish behave better when held in groups.
Examples:
Tetras
Rasboras
Barbs
Corydoras
Mollies
They become stressed by keeping them in pairs or alone, and thus fights start.
Repairs:
Keep schooling fish in a group of 6 or more.
They spread aggression within the group and remain themselves calm.
7. Feeding Appropriately to Decrease Aggression
Hungry fish are angry fish.
When the fishes don’t get enough to eat, they start chasing others.
Solution:
Feed small amounts 2 times a day
Provide a balanced diet of flakes, pellets, and frozen food.
Make sure food reaches bottom dwellers, such as corys
Well-fed fish fight less.
8. Maintain Good Water Quality
Dirty water is a stress factor, and stressed fish are aggressive.
Do this weekly:
Change 20–30% water
Clean glass
Waste removal
Rinse filter media in tank water-not tap
Clean water = calm fish.
9. Dim bright lighting
Strong light can make shy fish nervous, and aggressive fish hyperactive.
Solution:
Turn lights on only for 8–10 hours.
Add floating plants to soften light
A softer light environment makes all fish peaceful.
10. Temporary Separation of Aggressive Fish
If one of them is too aggressive:
Try these:
Use a divider
Move aggressive fish into another tank.
Put the bully in a “time-out box” (breeder box) for 1-2 days
This breaks their dominance and reduces their aggression when returned.
11. Dither Fish- Added special trick!
Dither fish are active, fast swimmers. They make active, aggressive fishes feel more secure.
They distract dominant fish from attacking tankmates.
Examples:
Danios
Tetras
Thorns
This works especially well in cichlid tanks.
12. Select Peaceful Beginner Fish
For the amateurs, their safest peaceful fish options would be:
Guppies
Platies
Mollies
Rasboras
Tetras
Corydoras
Otocinclus These species rarely fight and are easily kept happy.
⭐ Final Thoughts
Stopping fish from fighting is mostly about creating the right environment. When the tank has enough space, hiding spots, the right tankmates, and good water conditions, fish stay relaxed and peaceful. Remember: Happy fish = peaceful fish.