The world is now producing more farmed fish than beef. In 2012, fish production reached a record 66 million tonnes; cattle-farm output levelled out at 63 million tonnes. This ought to be good news for the environment. Cattle farming is one of the biggest contributors to global warming, while fish farming – as well as being sustainable – produces little pollution. Fish such as the silver carp can be reared on existing rice paddies, and they feed on grass, plankton and detritus. Species such as salmon, however, are carnivorous and are fed on smaller fish like anchovies caught in the wild. As a result, salmon can only be farmed by further depleting wild fish stocks.