According to a recent report by The WorldFish Center, with aquaculture on the rise, the question is how can we make sure that it doesn't put an undue burden on the environment, so that best practices are used and species groups are cultured that don't have excessive impact.
The report says fish farming can have environmental benefits if done sustainably. Fish process energy more efficiently than mammals such as cows and pigs because they are cold-blooded (so less calories are needed for warming themselves) and live in water (so relatively more of the body converts to muscle than bone). The authors say that for each kilogram of protein from beef, a cow needs to be fed the equivalent of 61kg of grain, for pork, a pig needs 38kg, but for fish it is just 13kg of grain. In addition, says the report, aquaculture emits less phosophorous, nitrogen and greenhouse gases than livestock farms.
However, it warns farming can have a greater negative impact if it focuses on carnivorous fish, which require food from outside the farm. There is a lower impact from herbivorous fish, or better still seaweed, mussels, oysters and molluscs.