Before placing different species of fish together in a fish tank, you must find out if they're compatible and can live together. Not all species of fish can live with each other. When fish aren't compatible there's the danger of them fighting with each other and even eating each other. When placing fish together in an aquarium, make sure that there's enough space for all of them, and that they require the same nourishment and the same water temperature. If they don't have enough space to move around, they may harm each other. It's also important to make sure to give your fish enough food [source: RSPCA]. You'll have the best chance of choosing fish that are compatible with each other if you consult an expert or a fish compatibility chart, which can be found online. However there are some general rules that indicate whether different fish are compatible.
- Don't put the two fish together in the same tank if one fish is small enough to fit into the other one's mouth.
- Don't put fish that look alike together in the same tank. The less alike two types of fish look, the more likely they will live peacefully together.
- Don't put fish that are closely related together in the same tank. The further apart two kinds of fish are in the fish family, the more likely it is that they will be compatible [source: Best Fish].
- Don't put aggressive fish in a tank with other fish [source: Fitzgerald]. Remember that even within a given species of fish, the temperaments of the fish may vary. This may lead to incompatibility [source: Pet Education].
