This is a good point. However, this problem is only in wild caught salmon from the pacific nortwest. Farmed salmon or salmon from other parts of the world are not affected. Freezing fish from the affected area for several weeks will take care of the problem. Most of the salmon bought in grocery stores are farmed unless otherwise stated.
Yes, you're right for the most part RFD. But the fisheries affected by this stretch from Northern California to Alaska, which is precisely where I fish most of the time (Nor Cal). Also, it is true that most store-bought salmon is farm raised, which I don't eat myself and which actually has quite a bit less Omega 3 compared to it's wild cousins. That is a controversial topic but the current data shows this to be true where only a few years ago the opposite was the prevailing wisdom, that fattier farm salmon had more Omega 3. Turns out they do have more fat but less Omega 3. Here's a great article on that subject.
Factory Farmed vs Wild Salmon | Mark's Daily Apple
Right now there is quite a bit of late-season wild Coho and Copper River King salmon in the markets (yum, yum!) so just be careful when you give salmon and steelhead to dogs because there is plenty of the wild stuff on the market in the summer.
It's also worth mentioning that almost all the trout you can buy in a market these days is farm raised. Too bad, there is nothing like a good wild trout for dinner. The meat is pink, like salmon. Not like the white, mushy crap they sell in most stores. But the farm stuff is probably safe for dogs whether raw or not.
Personally, I usually reserve the skin from the salmon I cook and give that to my dogs (cooked). It's rich in Omega 3 and they love it and since I don't like the skin, it's a win-win.
Cheers!
Jay