Aquarium Fish Compatibility and Incompatibility
Fish compatibility and incompatibility are often overlooked when it comes to fish choices for a home aquarium.
Most people just get whatever fish they want and put them into the same fish tank and be done with it. It can have potential consequences due to compatibility issues. Some fish should not be in the same fish tank. When the wrong species or incompatible fish are in the same fish tank, it can cause unnecessary stress to the fish, with the potential risk of injuries or even deaths.
Since there are thousands of fish species in the aquarium trade, we can’t discuss them all in one article. In the following, we will list some examples and give everyone a basic idea of what this compatibility issue is all about.
Same species incompatibility
Most people know we can’t put two male betta fish in the same fish tank because they will likely to fight to the death. People call them Siamese fighter fish after all. It is less known that even two female betta fish should not be in the same fish tank either. While it doesn’t happen all the time, some female betta fish can be just as aggressive as a male. In rare cases, female betta fish have even killed male betta fish. Thus, a male betta and a female betta are not compatible either except for the short window of the breeding season. Even then, you have to be careful and pay attention to their behaviors closely. Separate them as soon as there is a sign of aggression.
Some fish like most species of gourami are generally aggressive toward their own species as well. They are after all the relatives of betta fish. Not even a male and female should be in the same fish tank together. I would highly recommend not to have more than one gourami in the same fish tank.
German Blue Ram are generally peaceful fish. They can be aggressive toward their own species when it comes to breeding rights. If you have more than one pair in the same fish tank that is not large enough, the two couples might fight over territory for a breeding ground. In some less common cases, one male might try to take both females which makes the two males being aggressive toward each other.
The following video is a “fight” between two pairs of German Blue Ram over the breeding ground. They both want that big flat rock to lay eggs. While it might be fun to watch for some people, you do not wish such aggression in your tank as a daily routine. It is stressful for the fish, and it can cause injuries and deaths.
The peaceful German Blue Ram can also be aggressive toward other fish in the same tank when they are trying to defend their nest. They will attack any fish get close to their eggs. In such case, a separate breeding tank might be necessary if you do not have a large enough tank with relatively low fish density.
Inter-species incompatibility
One example is, Gourami and betta are also relatives. We should not put them in the same fish tank either. They are likely to be aggressive toward each other.
In general, it is not recommended to house any fish species that occupy the same water level as betta fish in a betta tank. While most people think the infamous Siamese fighter fish will be the aggressor, it is not necessarily the case. Since domesticated betta fish are the result of selective breeding, they have longer fin than their wild counterpart. A lot of fish species including generally peaceful tetra are nippers. Fish with longfin make the perfect target for nipping. Slow moving betta fish is more likely to be the victim in a tank full of fast-moving nippy fish.
Some people are keeping multiple female betta fish in a community tank and claim it is okay. While it might be okay for now, it is a ticking time bomb. All it takes for everything is fine to become not fine is one accident. You may try at your own risk. I would not recommend it.
Schooling fish compatibility
While there is the incompatibility issue, there is also this minimal compatibility issue. There are many schooling fish. When you decide to get schooling fish, you should get a school of them instead of just one or a few. In most cases, schooling fish species require minimal 5~6 of them to be in the same fish tank. They feel safer in number, and they are more likely to show their natural behavior when interacting with their species. If the minimum number is not met, they are likely to be shy, inactive, and stressed.
Examples of schooling fish are most species of tetra, such as Neon Tetra, Cardinal Tetra. There are also corydoras, rasboras, etc.
When you decide to get schooling fish, the more you get, the better. As long as you do not overstock your fish tank, the fish will enjoy the larger number.
Environmental compatibility
There are thousands of fish species from all over the world. The natural environment which they came from is apparently not the same. While most fish can adapt to some changes if given them time to acclimate, some changes should never happen.
Example: Goldfish lives in cold water. Tropical fish lives in warm water. In captivity, tropical fish require an aquarium heater to keep the water warm, usually around 72~82F depend on the species. Obviously, goldfish should not be in the same fish tank as tropical fish. They do not belong in the same environment. You can’t satisfy both fish at the same time if they are in the same fish tank.
Make sure your aquarium does not have any compatibility issue is one crucial step closer to have a perfect aquarium at home. It is the best to research the each fish species you plan to get. Including their natural environment and behaviors. Ask questions online if you are not sure about the compatibility.