With increasing population there is an increased demand for nutritious food. Seafood or 'blue foods' are in very high demand and we turned to farming to meet it. There are different types of aquaculture, such a offshore open pens, nearshore open pens and land based closed systems.
Out of the 3 mentioned, closed systems are the most sustainable. This is because the other two have issues regarding fish waste not being properly filtered due to the concentration, increase of diseases and introduces non-native fish and plants.
In a closed system, they use a barrier between the 'farm' and open ocean with reduces outside interaction and the spreading of dieseas. Using seaweed and shellfish help filter out the fish waste. They are often powered by renewable energy.