Would you (knowingly) keep mice and cats in the same room? It’s exactly the same with aquarium inhabitants! There are some predatory fish who would be very happy to have shrimp and small fish species as temporary roommates - until they’ve eaten them all. And there are fish that go together as well as noisy teenagers and delicate convalescents in need of peace and quiet. So it’s well worth knowing a little about fish socialisation, even if most do basically get along well.
Predators and prey
Large fish species usually eat small fish. There are exceptions to this rule, but you should know that your large cichlid, such as the angelfish or the cute-looking Oscar (Astronotus ocellatus) as a juvenile, will regard anything that fits in its mouth as food.
In your aquarium you have a ground floor flat that is perfect for all your bottom-dwelling fish. They aren’t really interested in who lives above them. So you can nicely occupy the middle floors, i.e. the free swimming space in the middle of the tank, with a school of fish. Just make sure that the school of fish has enough free swimming space. A completely overgrown aquarium means your free swimmers are constantly being confronted with obstacles. And the loft is reserved for the pure surface dwellers in your aquarium: Hatchetfish or small Pachypanchax species feel right at home there. And they, in turn, don't really care who their subtenants are...
Trouble in the flat share
As with humans, certain fish really don't get along with each other. The tiger barb, for example, is known to eat the long fins of other fish. So fighting fish, long-finned guppies and gouramis are absolutely unsuitable aquarium mates for them. Both parties, however, get along very well with other fish!
When the flat is too small
Cichlids in particular are very territorial. They claim a certain space and may defend it to the death against fish of the same species.
Different water requirements
Make sure that your aquarium inhabitants have similar water requirements. Most fish are happy with a pH value around neutral 7 and medium water hardness. However, fish like the cardinal tetra, for example, like soft, acidic water, whereas shell dwellers from Lake Tanganyika need hard, alkaline water. Your specialist retailer will certainly be happy to advise you on this.
If you ask an expert and read up about the fish species, you will quickly find out if your fish are a good match and if you’re providing the conditions they’re most comfortable in. Because that is always our goal, isn't it?
You can find more about planning and stock here: Planeamento e povoamento
You will find a brief outline of the different fish species here: Espécies de peixes