How To Choose Compatible Fish for Your Aquarium

Much like people, fish have very specific and various needs as well as temperaments. An environment that works for one fish won’t work for another, and not all fish will get along. To ensure you’re picking the right fish before you buy, here’s how to choose compatible fish for your aquarium.


When introducing a new fish to an existing aquarium, one of the most important factors to consider is the temperament of the current fish and the new one. Some fish are aggressive, while other fish are calm and prone to being bullied. Other fish are only aggressive when they don’t feel like they have enough room or are in a tank with the same species. For example, betta fish tend to be aggressive when kept with the same species but can do well with snails, fish, and specific frog species.

Fish Size

When it comes to the size of your fish, you need to consider how much room your fish have to swim. You also must not pair large fish with smaller fish because the bigger one may eat the smaller. For example, angelfish are not considered aggressive. But they are very curious and tend to put things they shouldn’t in their mouth. If they see a fish that is much smaller than them, they may be tempted to eat the smaller fish. As mentioned previously, some fish will be prone to aggression if they feel that they don’t have enough room. Being crowded with a larger fish may tempt other fish into fin nipping and bullying.

Aquarium Size

The size of your aquarium, as well as how many fish and how much décor you have in it, will greatly affect the amount of personal space your fish have. Even fish that are not territorial will become aggressive if a tank is too small and overcrowded. This also applies to certain species of corals with sweeper tentacles. If they do not have enough space, corals can hurt other corals and fish unintentionally. It’s important to talk to the salesperson about the specific needs of the species you intend to buy.


Gender is very important to take into consideration, especially if you want to use your aquarium for breeding. Some fish will be more aggressive to the same sex or the opposite sex, depending on the species. To use betta fish again as an example, female betta fish tend to get along with other females, while males tend to fight in the tank.

Now that you know how to choose compatible fish for your aquarium, you’re better equipped to set up a peaceful community tank with happy and healthy fish. Just make sure to always check with your salesperson and inform them of your existing tank mates if you have any questions.

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