Wild caught fish and seafood often has excellent nutritional value. However, caged salmon is not in that category. It is among the most unsustainable ways of seeking profit at the expense of the environment and possibly even consumers. Fattening a top predator like salmon in cages requires lots of feed, antimicrobial and other treatment to keep them alive in unnatural environments and pollutes the area around the cages. Salmon in cages on land would be the equivalent of raising lions for large-scale meat consumption by humans. Instead, we have cows and pigs and chicken, feeding in the bottom part of the food web, not animals at the top of the pyramid. Why, because only about 10% of the energy gets transfered from a lower to the next higher level in the food web. So if you start with 1,000,000 t of primary producers (gras, phytoplankton - plants that transform solar energy into organic body mass) 5 levels up in the food web where adult salmon would be, you get only 100 tons.

Incidentally, this is also why the biggest animals in nature feed low in the food web because that's where most of the biomass is. In other words, if we were managing fish responsibly, that is protect the juveniles and the highly productive big (though few) females, taking no more than 20% of the biomass of a healthy population that can regrow in a year, nature would give us plenty free of charge and without antibiotics.

Food for thought. There is more than omega 3 to be considered.