The nutritional case for farmed fish rests heavily on omega-3 content, but the wild fish caught for feed may have as much nutritional value lost as is created, alongside significant welfare costs.
The omega-3 argument for farmed fish consumption relies on a welfare calculus that is rarely made explicit: the nutritional benefit from one large farmed fish is produced at the cost of multiple small wild fish processed into feed. If those wild fish are sentient beings capable of experiencing suffering, the aggregate welfare cost of producing farmed fish omega-3 may exceed any benefit from reduced human cardiovascular disease. Plant-derived omega-3 from algae (the original source, from which small fish accumulate it through the food chain) provides equivalent nutrition without this welfare chain, representing a genuinely welfare-positive alternative.