Aggressive Fish

Fish compatibility should be measured in aquascaping. Putting fishes together in an aquarium does not guarantee that they will peacefully live together, so take time to learn which tropical fish can live together in a tank.

In this article, I will show you ways to make fish less aggressive on the rest of the post. To come up with the solutions, we need to identify where this bad behavior is coming from.

The Reasons Why Fish Become Aggressive

The following reasons are quite evident as a sign of aggression. Fights among fishes are so alarming, as damages are only seen when the fight is over. You are better off having ideas on where aggressive behavior is coming from. Let’s take a look at the following!

Feeding Jealousy

During mealtimes, fishes tend to eat everything that surrounds them as if their food is lacking. It causes aggression between the pets, which seems normal but a problem. It leads to damage when not amended immediately.


Some fish species are territorial. Introducing a new fish friend will never be a good idea with these kinds of fish. They treat the new pet as an invader in its space, which pushes the old one to act like a ‘boss.’

This behavior lasts for up to 8-weeks. Being territorial could be developed if the tank only contains two fishes from the start.


Fishes are like people; wherein when we get sick, everything annoys us. Some fishes do not show a lot of compassion to other species which are sick.

They make the situation even worse by attacking them. That is so cruel, but it happens in real aquatic life. It makes the fish’s recovery more difficult and may also infect others.

Personality Differences

Not all kinds of fish have the same personality and interests. Some can go along with many fish species, while others cannot. There are fish with bratty personalities too.

Other species are born to be bullies for no reason. Petting these pets together will cause so much trouble and stress to your tank.

Too Crowded Tank

Heavily stocked fish aquariums could be more prone to aggression unless they come from the same fish breed.

Most fish keepers do higher stocking densities to develop a social hierarchy, but the other way normally occurs. The pets pick on each other more often, maybe because of the crowded condition.


Love in the water results in being wild at times. Spawning fish are so disturbing to live with that they cause aggression among other fishes inside the tank.

You can easily spot the difference between spawning aggression and other aggressive behaviors by fish’s genders. There are appearance differences between male and female fish that are easy to notice. Spawning is triggered by the spring weather, full moon, and water change.

How to Lessen Aggressive Fish Behavior

After knowing why fish become aggressive, you can foresee strategies on how to deal with it. I searched for the ways most fishkeepers apply in aquascaping, but only five of them caught my attention. That includes:

1. Landscaping Techniques

One way to minimize fish aggression is by properly decorating their habitat with essential things.

Avoid putting materials with sharp or rough edges, for it may cause severe injuries to the pet. Put river rocks with pieces of driftwood as an alternative to providing individual territories among fishes. Check out the Zilla Reptile Décor Malaysian Driftwood, which promotes basking for the pet without scratching the aquarium.

Add some plants to break up sightlines, which is a common cause of aggression between fish. Live plants promote a natural habitat for fish and help to oxygenate the tank.

The problem is that it can be easily uprooted by large fish that turn into their food source. Synthetic plants could be your alternative. You may plant SunGrow Aquarium Grass Seeds that soon create a green carpet plant with minimal maintenance.

You may also include other hiding places in the tank. As females are at liberty to find their territory, males will be greatly benefitted from the setup. VORCOOL Sea Rock Cave Ornament could be the best choice as a hideout for the fish.

Make sure to incorporate those stuff with an aesthetic appeal, not just pieces added. You can alter the terrarium arrangement for better results. Your goal is to keep the fish in a healthy environment, just like their natural habitat.

2. Separate Non-aggressive to Aggressive Fish Species 

This strategy should be done from the very start of aquascaping to have a fresh start. Doing the separation the first time you plan to care for fish is advisable to prevent future damage among the pets. You can search which fish species are aggressive and non-aggressive to finish the setup.

Below is a partial list of aggressive and non-aggressive fish species you might plan to care for. If you are still in doubt, do research over again and find out for yourself.

List of Aggressive Fish Species

  • Cichlid

Some cichlids are quiet and calm, but some are territorial. They attack and even kill new invaders to defend their territory. Male cichlid turns to be aggressive towards females who do not want to mate.

  • Dogtooth Tetras

Their huge teeth frighten small fish. They are considered devil carnivores, which sounds scary and very alarming. Dogtooth Tetras often swallow their prey into pieces. Even humans could be in danger of taking care of this fish species.

  • Tiger Barb Fish

Tiger Barb Fish’s looks might be deceiving, as they look beautiful but has dishonorable nature. They tend to be aggressive to smaller species that cause them death. An omnivorous diet is what applies to tiger barb fish, wherein anything is edible for them.

  • Gouramis

Hiding spots are necessary for taking care of gouramis. They might be small in size but may torment other species. Weaker fish species are their primary target to put in danger, which sometimes leads to death. Gouramis are labeled as semi-aggressive as they can be friendly at times.

List of Non-aggressive Fish Species:

  • Danios

Danios promote peace in the aquarium, especially between male and female betta. They also look beautiful and can be bought at an affordable price.

  • Guppy

You can buy guppies in a bunch at a very affordable price. They are suitable to live in a group of the same species. Guppies are very friendly and eye-pleasing. They can live longer than any other fishes.

  • Koi

Koi lives in a pond because of their bigger size. In spite of its hugeness, koi are kept at ease in their habitat. They can thrive for up to 100 years with due care. Paying extra in buying pure koi is not a surprise anymore. Some breeds are sold at a lesser cost, but they are not pure.

  • Neon Tetra

Keeping fish of the same breed is advisable for beginners. Neon Tetras are the happiest living in a group, so they are the best option to care for. Adding more and more of them in a tank will never be a dangerous act.

The list goes on as you browse the internet. Asking aquatic experts is advisable to know more about fish species. Do not buy fish right away without knowing its personality and basic needs.

3. Use a Floating Box

A floating box is useful during feeding time. It isolates the bullies from causing trouble to other fish species. Those fish calm down after being released out of the floating box.

PETS ISLAND has to offer Aquarium Fishes Breeding Boxes to protect newborn fish from adult ones. Its other function is to separate aggressive fish from non-aggressive species. It also serves as an incubator for pregnant fish.

The Isolation Box will not occupy much space inside the tank. The box has an invisible ventilating hole to prevent fish from escaping. Its self-floating design makes it suitable for any type of aquarium. It can be fixed anywhere inside the tank for convenience.

Another best-seller is the Fish Breeding Box made by capetsma. It can be assembled within minutes with three easy steps. It floats independently without occupying so much space.

It has a balancing board and two handles to avoid sinking. Choose between three sizes according to your needs. The isolation gap allows water flow while preventing fish from escaping.

Overall, floating box isolates fish prone to danger. It, therefore, increases the improved living rate of fish even when living in a group. This aquarium add-on is multi-functional that greatly benefits fish.

4. Add a Tank Divider

If temporary separation did not work to lessen aggression, maybe a tank divider will make a difference. In this way, you won’t be buying another aquarium for the sake of aggressive fish species. A separator is enough to prevent commotion among the pets. This strategy is applicable in the long run.

Four pieces of aquarium divider are more than enough to begin separating fish species. As I browse online, Chnee’s tank divider caught my attention.  They used food-grade plastic material in creating fish tank dividers.

It won’t affect water quality and so great for fish’ wellbeing. You can separate the tank into sections for breeding and other fish activities. The purchase includes eight sucker clips to fix the divider anywhere in the tank easily.

The grid divider increases the survival rate of newborn fishes, sick fish, and non-aggressive fish species. It prevents the fish from biting each other when aggressive behavior hits them. Its holes are not big enough to let fish live together.

Some tank dividers are made of acrylic. They are easier to clean with soft cloth scrub. It uses up a suction cup to keep it in place inside the tank. The small holes do not allow fish to go through it. Acrylic tank dividers cost higher than grid dividers.

5. Clean the Water Regularly

An unhealthy environment could affect fish’s activities as a result of produced ammonia. It comes from waste, particularly with uneaten fish food that hoards at the bottom of the tank.

It is essential to remove debris to keep the water quality healthy for fish. Cleaner water helps to lessen fish aggression.

Here are cleaning materials you should use in cleaning a water tank:

Fluval Biological Cleaner for Aquariums

Heavily populated aquariums are to whom the biological cleaner is made. It protects any kind of fish against ammonia and nitrate. The cleaner also reduces organic waste produced by the pets.

Most fish keepers use the cleaner in cleaning decorations, filters, and other surfaces. Daily maintenance is reduced by using a cleanser as such. It is suitable for both freshwater and saltwater tanks.

COODIA Aquarium Sterilizer

Green water is not suitable for fish and needs to be cleansed. This submersible disinfection pump can clean up to a 150-gallons aquarium, both saltwater and freshwater.

It is easy to install in tanks with suction cups. The water outlet is adjustable for better use. The pump generates an air bubble to the water that adds beauty to the tank.

Fluker’s Eco Clean All-Natural Waste Remover

The foul-smelling tank will turn into a hygienic habitat for pets with the use of waste remover. It is explicitly formulated for aquatic reptiles and amphibians. The formula eliminates solid waste caused by bacteria and enzymes.

The amount of dosage differs for first-time use and maintenance.  Lesser dosage is required during maintenance, which is done once a week. It is all-natural and so safe for pets.

Check online for more water tank cleaner! As water is the primary source of survival for fish, it should be kept clean at all times.

Final Words

To summarize, it is hard to discern how fishes are going along with the other fish in just a glance. Some species are so deceitful and act kindly when someone is watching but become aggressive later on. Among the five ways to lessen fish aggressive behavior, try the remaining ways if one did not work.