This is nonsense, if I want to have salmon buttons on my waistcoat, jacket, or anywhere else, I can do, simple as that.
If I am copying exactly an image of a particular salmon that someone else has the rights to, that of course is something else. If I am trying to pass myself off as someone else by the use of some decorative device ,that too is wrong.

as Matt said :
I wonder if this is just a "stongly expressed opinion." I mean, what jurisdiction does the Lyon Court have over non-heraldic dress and accessories, really?

The simple answer is that it doesn't have any jurisdiction.

If anyone of us want to use artistic and/or decorative images as buttons or decoration, then we may. Of course some may question taste or style, but there is no "law" to prevent us