I have a cat that "plays with" Sun Ce periodically. She paws at the tank, and Sun Ce will swim back and forth in front of her paws. Of course, Ciani (the cat) is trying to get at the tasty morsel, but Sun Ce doesn't know that.
Other than that, Sun Ce's interaction usually comes from water changes, feeding, and random tank maintenance. He's also got a ton of vegetation in the tank, so he's got lots of stuff he can explore. The water wysteria grows really quickly, so the tank layout is always changing.