Although an Oscar fish can be aggressive, he will share his tank with other fish. In particular he is suited to fish around his own size who are neither too passive nor too aggressive. Like many species, however, every Oscar is different; some are more aggressive than others.
Choosing the Right Fish
You can put other fish in an aquarium with an Oscar fish, but remember if a fish can fit into his mouth, they are a potential meal.
As a general rule, Oscar fish will live with most other cichlids that are similar to them in size. However, the best fish to put in with them is the silver dollar fish. Silver dollars are large, quick and even enjoy cleaning up after the Oscar has left a mess after a meal.
Do not put small to medium catfish in with an Oscar fish. If he tries to eat them, their spines will get caught in his mouth and eventually kill him.
Finding the Right Size Tank
You must ensure that your tank is large enough for multiple fish. If you add fish to an Oscar's tank that is less than 70 gallons, your Oscar will most likely bully and kill them.
The suggested tank size for an Oscar fish on his own is 55 gallons, but he will likely out grow that when he is his full length of 12 inches. To be on the safe side, and certainly when you put other fish in with him, you should purchase a tank that can hold more than 70 gallons.
Feed Well
You need to provide your Oscar with a well balanced diet. In nature, an Oscar will eat other fish, insects and worms, but he will also eat fruits and vegetables. Supplement any food with high quality fish pellets. As your Oscar matures to his full length, you will need to feed him larger treats such as raw shrimp.
If you feed your Oscar well, he is more likely to stay away from any fish you put in with him.
The Last Resort
Oscar fish can be hard to predict. If you notice your Oscar fish acting overly aggressive to the other fish, remove him immediately from the tank and house him in a separate aquarium. Mostly he will fight fish for territory and food. If he is well-fed and has plenty of space to move, he should not provide any problems.
