Yes, and that is not the kind of aquaculture I have in mind. Instead, you pick a large area in the high seas, and trigger a permanent algaebloom by seeding micronutrients (Iron, mostly), then either you have floating clambeds or a stock of shrimp to eat the algae. Fishfarming as done near shore involve feeding the fish directly - the idea here is to manage a (short) foodchain from photosynthesis to supermarket counter.