“Some of the most valuable farmed species, like salmon and trout, are carnivorous and must be fed wild-caught fish when farmed. Farmed shrimp, along with a number of omnivorous fish species, are also fed wild-caught fish. All told, some 17 million of the 91 million metric tons of wild-caught fish are diverted to the aquaculture industry annually.”
https://www.vox.com/future-perfect/379564/fish-farming-sustainable-wild-caught