Orca are fish because they live in the sea.

Original Text From Meme:

Orca are fish because they live in the sea.
Orca are whales because they're big sea mammals.
Orca are dolphins because they're in Delphinidae the dolphin family.
Orca are whales because they're in Cetacea the whale infraorder.
Orca are fish because they're in Osteichthyes the bony fish superclass.