I have some plants and ornaments in with Eddie, if anything, he likes the plants. He'll sit in them, or hide behind them and peek out at me.
For a while he was obsessed with the filter, he'd ride the current down, swim up and back into it again, over and over.
He does seem to love flaring at a green pen I have too.
Fishy-san before him seemed to love the little bridge. He'd always squeeze under it and poke his head out.