"I work on what’s called a “recirculating” aquaculture farm. We’re still trying to maximize fish production, but we deal with the waste problem by closing the loop, doing our own water treatment on site and re-using as much of the water as we can. We have very high stocking densities -- let’s say twenty to thirty thousand fish, in tanks the size of swimming pools. Dozens of these tanks can fit together within one warehouse building. The water they swim in is constantly flushed out, filtered or treated in several ways, and pumped back in clean. The solids that are removed in the treatment process are stored and sold for fertilizer. So the water in the tanks “recirculates,” in parallel, and the tanks share a number of supplementary systems that help maintain an optimal growing (“culture”) environment: heating, feed, chemical regulation, and so on. We grow them for about a year, with each fish ending up as about a pound of meat when fileted. The idea is that this basic design can be scaled up to make really huge farms. Ours is a really huge farm."
Red Herring, fish farmer interviewed by Flint Arthur