Unfortunately, a lot of farm-raised fish are fed smaller fish from natural ecosystems, effectively shifting but maintaining the overfishing problem.

If you care about omega-3 (you probably should) without contributing to overfishing (again, imho you probably should), get an algal-oil based supplement. Prices are pretty competitive nowadays.

Good thing about farm-raised fish is that it is less contaminated, because it is usually mostly plant-fed. But it also makes it less nutritious.

Salmon is found in high-latitude systems around the globe in both hemispheres. Overfishing is something that occurs to populations, not species. Most of the salmon populations that I am familiar with are not over-fished, but have suffered from spawning habitat loss due to dams and logging. Those are major issues and they continue to negatively affect those populations; you are doing the loggers and dam builders a favor by blaming fishing, which is far easier (and more politically palatable) to regulate.