How many pounds of anchovies does it take to produce
one pound of fish-farmed salmon?

"The salmon-farming industry requires an enormous amount of food. And with salmon a lot of that food consists of other fish that are harvested from the wild. In an unimproved state, farmed salmon require as much as six pounds of wild fish, ground up and turned into pellet feed to produce one pound of edible flesh. Selectively bred salmon, meanwhile, have reached a point where less than three pounds of wild fish can produce a pound of salmon." -- Paul Greenberg. Four Fish: The Future of the Last Wild Food. NY: Penguin, 2010, p. 44.

Still Life with Anchovies, 1972
Antonio Sicurezza
Wikipedia