Crowding

Stocking densities (the number of fish per cubic foot of water) on fish farms are constantly raised until the death losses outweigh the financial benefits of cramming more fish into a smaller space. Salmon farms are so crowded—with as many as 50,000 individuals in each enclosure—that a 2.5-foot-long fish spends his or her entire life in a space the size of a bathtub; trout farms are even more crowded, with as many as 27 full-grown fish in a bathtub-size space.