My two favorite fish. Nice picks.
Black Ghost Knife tank mates:
Stay away from bottom dwellers and fish that can fit into its mouth.
Angelfish & a Pleco are the most ideal tankmates.
Oscar tank mates:
Aother Oscar *(Work best if they have been together since they've been little. Sometimes this goes wrong)
3 large cichlids (12 inches), 5-6 medium cichlids(6-8), or between 10-15 small cichlids (3-5)
For more detail about oscar tank mates I'd visit here: