Salmon is generally considered by kashruth authorities to be distinctively identifiable as kosher from the appearance of the flesh. Nonetheless, I've noticed that the local Costco sells (side by side) certified kosher and uncertified, fresh, precut, packaged, farmed salmon. What, if any, are the halachic advantages of buying salmon certified as kosher, rather than cheaper and/or fresher uncertified fresh salmon, from Costco? Is there a halachic concern, even in the current allergen-conscious age, that a mass producer of salmon (such as the one supplying Costco) would be using equipment contaminated with nonkosher species such as shellfish?
R Sholem Fishbane, the Executive Director of the Associated Kashrus Organizations (AKO), an umbrella group of major kosher-certifying agencies and the and the Kashruth Administrator of the CRC kosher supervising agency spoke to the Headlines podcast about this.
At 1h43m here he explains salmon can be purchased without supervision. He says "at most, to be truly machmir you can do shifshuf (rubbing) of the place which was cut". He explains there is no need to remove a klipa of fish since there is no blia (absorption). He speaks of fresh salmon being cut in front of you with knives that were possibly used to cut non-kosher fish. Once you accept the ruling of the OU (which you quote in your question) that pink-looking fish is kosher, then I don't see a difference between freshly cut and packaged.
But don't take my word for it ...
OU Kosher writes
The factories which produce both wild and farmed salmon produce copious amount of fish every day, and even if there was a non-kosher product cut with the same knife, the non-kosher residue on the knife would be wiped off on the first few pieces of fish cut with that knife. Those fish would be mixed in with thousands (or tens of thousands) of other salmon, which would be perfectly clean of residue, and become nullified (batul). The Shulchan Aruch (YD 96:4) rules in the case of lemonade and salted fish that all of the product is permitted, despite the non-kosher knives involved. The Rama explains this is due to the large amount of product cut with the same knife.
The Sephardic Halacha Center writes
In the case of a large-scale factory that processes only kosher fish with skin (such as a facility that packages salmon), the Aharonim are lenient and do not require the utensils to be certified kosher, as the possibility that they were used for a non-kosher items is remote, and even in such a case the small amount of non-kosher residue would be nullified in the vast amount of kosher fish that are being processed.