I heard once that some steaks sold are actually separate pieces of meat glued together and made to look like a natural steak. Maybe this happens with fish as well. Wouldn't "the entire fish is salmon" be referring to that there's no pieces of other fish glued to the fillet? I mean, perhaps there's a legal technicality where it's permissible to sell a product as salmon when at least 10% is actual salmon or so.
It's kind of like how all those sweeteners sold as being stevia are actually only like 1 or 2% stevia.
Sometimes they add filler to match the volume of sugar for equivalent sweetness. This makes it easier to proportion out for baking and adding to drinks. Otherwise the baking might be off or the drinks too sweet.
https://en.wikipedia.org/wiki/Transglutaminase#Industrial_an...
"For example, there was a poster of dried shiitake mushrooms that were slightly damaged during the production process. In the Japanese market, only perfectly round shiitake were sold, but MUJI sold imperfectly shaped shiitake because they taste just as delicious. In another poster, the copy reads “The entire fish is salmon.” This is straightforward copy reminding readers that salmon is delicious head to tail, so all of it should be eaten. Even as the Japanese economy moved closer and closer toward an economic bubble, we had positive feedback from so many consumers back then who wanted to focus on the simple things in life." https://www.muji.com/us/flagship/huaihai755/archive/koike.ht...
It shows that you can package almost anything as long as you do it with conceptual integrity. If you sell discounted goods, don't try to pass it off as as good as something more expensive, because that is not credible or interesting. Emphasize that it's less expensive, and why. When I google "conceptual integrity" which is funny in a way because I'm not a developer, and also interesting because it shows that many foundational ideas are cross-disciplinary.