There's the question of what inputs are used to provide the feed to grow the fish. E.g. for salmon > On a dry-dry basis, 2–4 kg of wild-caught fish are needed

There's the question of what inputs are used to provide the feed to grow the fish. E.g. for salmon > On a dry-dry basis, 2–4 kg of wild-caught fish are needed to produce 1 kg of salmon. The ratio may be reduced if non-fish sources are added. Wild salmon require about 10 kg of forage fish to produce 1 kg of salmon, as part of the normal trophic level energy transfer. The difference between the two numbers is related to farmed salmon feed containing other ingredients beyond fish meal and because farmed fish do not expend energy hunting. https://en.m.wikipedia.org/wiki/Aquaculture_of_salmonids https://en.m.wikipedia.org/wiki/Aquaculture_of_salmonids