The 3D-printed salmon hitting American grocery stores has zero salmon in it. It's a plant-based patty. And three years ago, the company selling it was printing fish fillets out of real fish cells grown in a lab. Its stock is down 99.9% since it went public. So what happened? Start with why anyone would bother printing salmon at all. It's one of the hardest foods on earth to fake, and you can see the reason right on the fillet. A salmon fillet is a stack of W-shaped muscle blocks, and those…