Back in the early 90's some people did some experimentation with rasing butter lettuce over some tilapia tanks. The heads of the baby lettuce were floated in small styrofoam rings and they were growing exponentially for a week or so and then everything went south. The tilapia stopped feeding on the pelleted food and the lettuce stunted and died.
Turns out the tilapia were eating the suspended roots off the lettuce!
I worked at an experimental indoor tilapia facility years ago up in North Dakota. We were set up to raise about 2 million lbs of fish a year. Another company was researching a way to use the waste water from our facility to raise hydroponic hothouse roses. From the wastewater they figured they could plant 18,000 acres of roses! Nothing ever came of it, though.