Farmed fish can be on par with wild fish (healthier in some ways, less nutritious in others) depending on the farming methods, which have improved since the old days.
Maybe less mercury, but by definition the fatty acid composition that makes fish healthy should be much inferior since algae are lacking from the food chain.
http://sciencenordic.com/how-healthy-farmed-salmon
I'd wager that fish from modern farms will soon be healthier (statistically) than wild fish caught in increasingly polluted oceans.