In the larger Freshwater Fish Compatibility Chart here, you can see you have many options when combining freshwater fish in your tank. Be sure to zoom in on the chart to see a clear view.

By making sure the fish you add to your fish tank are compatible first, you'll avoid future problems. Looking at the full-grown size of the fish helps too. You wouldn't want to add Oscars with Guppies, Danios or Minnows. Usually you'll keep varieties of the same family together as in a Cichlid aquarium. I've always chosen to stock my fish tank with semi-aggressive fish, but if livebearers are your thing... Great!

Using a Compatibility chart for Freshwater Fish to get educated, and understanding which fish you can mix and match in your fish tank, will save you questions at the pet store.

via: Habitattitude and Petco Freshwater Fish Compatibility Chart