Yet despite the growing popularity of farmed carnivorous fish, there has been no corresponding boom in catches of the food they eat. The world's catch of “industrial” fish—mostly anchovies, sardines and menhaden—that is used to make fishmeal has remained resolutely stable at 30m tonnes for decades. The reason for this mystery is that in the past fishmeal was used to feed animals such as poultry and pigs, but this has been cut back. Many argue that using fishmeal to feed fish is, in fact, more efficient than using it to feed terrestrial animals. Today, fish farms use about 40% of the world's supply of fish oil, and 31% of its fishmeal. Many, including theFAO, predict a worldwide shortage of fish oil within the decade.