PCBs and organic contaminants. The Hites et al. (2004) study in Science remains one of the most comprehensive global assessments of farmed salmon contamination. The researchers analyzed 594 farmed and 135 wild salmon samples from 16 cities across North America and Europe. Concentrations of 14 organochlorine contaminants were significantly elevated in farmed salmon, with PCBs averaging 36.6 ± 4.5 ng/g wet weight in farmed versus 4.75 ± 2.38 ng/g in wild Alaskan chinook. Using EPA risk-based consumption guidelines, the authors concluded that farmed salmon consumption should be limited to no more than one meal per month for some sources (particularly Scottish and Faroe Island farmed salmon), whereas wild Pacific salmon could safely be consumed at 8 or more meals per month [1].
Hamilton et al. (2005) extended this analysis, examining not just organochlorines but also the risk-benefit tradeoff of omega-3 consumption versus contaminant exposure. They noted that while all salmon provides beneficial omega-3s, the contaminant burden in farmed salmon partially offsets these benefits using standard risk assessment frameworks. Importantly, contaminant levels varied by region: South American farmed salmon had lower contaminant loads than European farmed salmon, reflecting differences in feed sourcing and environmental regulations [2].
Declining omega-3 levels in farmed fish. Sprague, Dick, and Tocher (2016) analyzed the fatty acid profiles of farmed Scottish salmon from 2006 to 2015. Over this period, the proportion of marine-derived ingredients in salmon feed dropped from approximately 80% to 40%, replaced primarily by rapeseed (canola) oil and soy-based products. This substitution resulted in farmed salmon EPA+DHA levels declining from roughly 2.7 g per 100 g flesh to approximately 1.4 g per 100 g — a reduction of nearly 50%. The study noted that while farmed salmon still contains more total fat than wild salmon, the omega-6 to omega-3 ratio has shifted unfavorably. In 2006, consumers needed one 130 g serving of farmed salmon to meet the recommended 3.5 g/week of EPA+DHA; by 2015, they needed two servings [3].
Antimicrobial use in aquaculture. Done, Venkatesan, and Halden (2015) conducted a systematic review of global antimicrobial use in aquaculture, estimating that approximately 63,200 tons of antibiotics were used in animal production in 2010, with aquaculture accounting for a meaningful and growing share. The most commonly used antibiotic classes include tetracyclines, sulfonamides, and quinolones. The review highlighted that in countries with less regulation, antibiotics are frequently used prophylactically (preventively) rather than therapeutically, accelerating resistance development. Residues of antibiotics have been detected in commercially available farmed fish in multiple studies. Norway stands as a counterexample — through mandatory vaccination of farmed salmon, the country reduced its aquaculture antibiotic use by over 99% between 1987 and 2013 while dramatically increasing production [4].
These findings collectively suggest that while farmed salmon is not inherently unsafe, the source and production practices matter significantly. Consumers benefit from seeking out farmed fish from operations with transparent feed sourcing, low antibiotic use, and third-party certification.