Well, it's a terrific idea. They can "farm" some oceanic stuff that can be destructive to catch naturally(blue crabs, yadda yadda). It's amazingly productive per square foot. It's reliable and consistent. All good stuff. It struggles commercially where most things like that struggle though - the capital investments are huge to get it off the ground, those buildings and the equipment is expensive considering the expected rates of return. The bigger issue though is you wind up having to do a lot of the work that nature would do for you in open-sky agriculture or fishing(related industries) yourself, so the energy and manpower costs stay high. Feasible and neat, but for the most part on staple goods instead of niches, not really competitive at this time. If this makes sense. Same sort of problem that getting biofuels from pond-scum runs into. Absolutely awesome in theory, not practical in large scale in practice with presently known technology and techniques.