Community Fish Compatibility Explained

Community fish compatibility is extremely important for a successful and healthy aquarium.

Before you start buying new fish friends for your aquarium you need to familiarize yourself with different species of fish.

You can not put incompatible species together as that will increase stress in your aquarium. Which could result in disease, injury, or loss of fish.

There are several factors that will decide whether you are gonna have happy fish friends or not. Let’s get started with this article about community fish compatibility.

1. Types of Community Fish Aquariums

Community fish aquariums can be separated into three different types of aquariums. This goes for freshwater and saltwater aquariums.

  1. Passive community fish aquarium
  2. Semi Aggressive community fish aquarium
  3. Aggressive community fish aquarium

1.1. Passive community fish

are often schooling fish or solitary fish and are not a real threat towards other fish in your aquarium as they usually do not eat other fish. They will do very well with almost any other fish that does not kill or harass your peaceful fish.

1.2. Semi Aggressive community fish

Community Fish Compatibility - Community Aquarium

can be aggressive or passive depending on your other fish friends in your aquarium. When you mix semi-aggressive fish with passive fish there can be an increased chance of your passive fish being stressed out.Semi-aggressive fish tend to engage in harassing smaller and passive fish which can lead to the death of your fish. It is best to add semi-aggressive fish when they are young. That way they can grow up with your other fish friends.

1.3. Aggressive community fish aquariums

might not be for everyone, they are extremely territorial and do not play well with your other fish friends. Plants are also not safe for aggressive fish as most will tend to destroy, eat, or uproot the plants.

2. Aquarium Size

Everybody needs space to move around and the same goes for your fish friends, different fish like different swimming spaces and shapes.

Try to pick fish that swim on different levels of your aquarium that way you avoid a traffic jam inside your aquarium and your fish can swim around with enough space.

Community Fish Compatibility - Space
This fishbowl does not have enough space

Wider aquariums give fish that are active space they need to spread out and the more space the better your fish will tend to get along.

Narrow aquariums are handy and fit in narrow spaces which also makes them very appealing to the eye. These aquariums do not offer much space and are used for less active fish.

3. Fish Size

Always buy fish that are roughly the same size as the ones in your aquarium. A fish will eat anything if it thinks it can get it in its mouth, and in a lot of cases, this includes the fish’s own young.

Community Fish Compatibility - Size

Even fish that is considered peaceful will try to eat other fish if they think they can, also when a fish gets large it will likely eat other fish that remain small. This is not because the fish gets mean as they grow older but they simply see the little fish as a potential yummie snack.

Keep in mind that if you are gonna start mixing territorial fish that newcomers should be close to the same size as your most aggressive or largest fish in your aquarium.

4. Gender

Gender is a very important factor if you are going for a semi-aggressive aquarium or an aggressive aquarium.

When you put too many aggressive male fish in your aquarium you will create a very aggressive aquarium. It is best to keep a higher female to male ratio around 2 to 1 when it comes to semi-aggressive aquariums or aggressive aquariums.

Community Fish Compatibility - Gender

For cichlids, this is very true. It is important to keep livebearers in a ratio of 2 to 3 females per male. This will lower the persistent mating behavior of the males. Because cichlids are aggressive try to avoid having more than one male of the same cichlids’ species. Also, avoid other territorial species or closely related to the cichlids’ species.

Sometimes it is best to keep aggressive male fish as a solitary species. Male fish have a tendency to be more aggressive and territorial. Especially around mating time, some fish will be left out from the mating and as a result, they can become aggressive.

For passive aquariums and schooling fish, the sex ratio does not seem to matter much.

5. Water Temperature

Community Fish Compatibility - Thermostat

Keeping fish with a significant difference in temperature can end up in trouble for your fish friends. Fish that require cooler water may suffocate or have trouble breathing from lack of oxygen because warmer water carries less dissolved oxygen.

It is also important to watch the water temperature in your aquarium because if the temperature is wrong your fish friends can refuse to eat, move slowly or catch a disease faster.

6. Feeding Requirements

Be aware of any feeding requirements before you buy any fish. A lot of fish will do perfectly fine with a wide variety of meaty food.

Community Fish Compatibility - Fish Food

Most will even appreciate algae and vegetation in their food as well as pellets and frozen food. But some of your potential new fish friends have very specific feeding requirements.Check with your local specialized store in aquariums on the correct feeding requirements for your fish friends.

7. pH Levels

Although most fish will do perfectly fine in a broad range of pH levels as low as 6.5 and going up to 8.0 it is very important to understand the pH levels of your aquarium water. If anything changes in your pH levels you want to act correctly to save your fish friends.

When you are going for an aquarium with live plants you need to take the pH level of your plants into consideration as well. Most freshwater plants need a pH level between 6.0 and 7.5.

8. The Temperament of Your Fish

Community Fish Compatibility - School of red-bellied piranha

Even if aggressive fish (or smaller) and peaceful fish are the same sizes it is asking for a disaster when you keep aggressive and peaceful fish together. The aggressive fish will keep your peaceful fish away from food or possible hiding places which will cause your peaceful fish friend to resist diseases less or possibly die from malnutrition.

Pick fish that have similar movements as well. Fish that are fast will chase fish that move slower.

9. Hiding Spots For Your Fish Friends

Providing your fish friends with hiding spots is a must even if you are sure that your fish will get along.

Community Fish Compatibility - Fish Hiding

Some fish just want some alone space and others do not feel safe unless they can hide somewhere. Not enough hiding spaces within your aquarium can lead to becoming your fish stressed, and you do not want that.

10. Mixing Freshwater and Saltwater Fish

You cannot mix freshwater fish with saltwater fish and vice versa. You either have to go with freshwater or saltwater.

Community Fish Compatibility - Clownfish Nemo

A goldfish, for example, would not like an aquarium that is suited for a clownfish (Nemo) nor the other way around. A goldfish needs freshwater and colder temperatures and will not live long in a saltwater aquarium. Also, the aquarium filtration equipment and pH requirements are different. If you want freshwater and saltwater fish the only thing you can do is to buy 2 aquariums. 1 freshwater, and 1 saltwater aquarium. But mixing is just not an option.

11. Stressed Fish

Overstocking your aquarium can make your fish feel stressed out. They need space and will often feel cramped up if there are too many swimming around. Adding the wrong kind of fish will also stress your fish out.

Your fish will tell you if they are not doing well. They will start to look pale, show signs of injury, refuse to eat, or leave their hiding spots.

Community Fish Compatibility - Fin Rot Betta
Betta With Fin Rot

Therefore, keep an eye out on the behavior of your fish because stressed fish can lead to health complications that are serious and may cause your fish to develop diseases that are fatal like Fin Rot.

12. Compatibility Charts

Choosing new fish friends can get tricky, especially for those who are new to the hobby. These compatibility charts can help you choose to pick out your new fish friends from the most common types of fish.

Keep in mind that there are no guarantees that can be made, each fish has its own personality and may not correspond with the charts above.


Take your time researching community fish compatibility to match the fish you like for your dream aquarium. Read as many possible sources as you can.

Try not to take the advice from an employee from a local fish/pet store though, as they often but not always provide incorrect information.

Even though their intentions are well it is best to go to a store that is specialized in keeping aquariums. This will make your aquarium stable and minimize the loss of your fish friends.

Thank you everybody for reading my article about Community Fish Compatibility.

If you have any questions about community fish compatibility, please leave them below in the comment box and I do my best to answer them all 🙂

  1. Thank you for this information. Little did I know that the types of fish we put together in an aquarium matter to the health of the system. If I understand you correctly, passive fish and aggressive fish should not be put together in an aquarium. Please may I know the types of fish that are aggressive, as I will like to avoid them in my aquarium? Also, which type of fish will you recommend I add to my freshwater aquarium that presently has only 3 Cory Catfish.


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