how so?

...how?

There's a kind of a compromise going on here. Wild Salmon stocks are limited and were it not for farming demand would outstrip what's available. Apparently the tradeoff here is "dead zones" in the ocean unfortunately.

Of course, as I say, the farmed salmon is not the same fish as the wild one. The flesh is dyed pink. The flavour doesn't benefit from the wild salmon's varied diet, and the texture isn't developed by all that swimming upstream.

There is a very wide variance in the quality of farmed salmon too, to the point where you really can't be sure what you're eating unless you actually know the farm it's coming from.

I've heard it said that farmed salmon carries little of the health benefits of wild salmon. Personally I'd prefer to just pay a lot to eat salmon very rarely than to eat farmed salmon frequently. But everywhere you go there is otherwise indiscriminate demand.