Salmon skin? Interesting. I don't know if this is something I could jump on board with. As a fashion designer, and environmentally-friendly and aware individual, I believe this would be a fashion crime!
Salmon are actually going into extinction territory. There are several companies and conservatories working on ensuring the salmon continue to repopulate and follow their usual upstream trail. I would hate to find out that the fashion world had anything to do with this problem becoming larger.
Whether or not they are tougher than calfskin is yet to be known. I doubt they are tougher, but they would definitely have a varied texture. It would be interesting to see, and a definite distinct shoe, but not worth the price it would cost.
Of course, this is just my opinion and understanding on the matter. I know Mizrahi is an understanding and conscious designer. He may be taking the salmon from a created hatchery or something that would not be harmful to the environment. In that case - have at it and happy shopping salmon everyone!!!