I wonder how this affects the fish's slime coating, which is important to preserve. It seems like this would be rubbed off on the material as the fish is propelled along the tube, no?
I'd be more worried about disease propagation. Would need to be self-cleaning, methinks .. super-clean the pipe in between fishy-pilot takeoff with a super-steaming? Hmm .. Combine the two, and we've got lunch. :)
It seems unlikely that they're going to be exposed to anything in the tube that they're not already exposed to when they congregate together at the bottom of a dam (or a natural waterfall). They can get pretty packed..
As another poster noted, at this stage they're not likely to live long enough to develop most diseases.
They can create more just as your body would create scar tissue if I scraped some of your skin off. Meanwhile, the exposed area is far more likely to become infected as your skin no longer protects it. Not a perfect analogy but it illustrates my point well enough.
Since this is to help them on their final stage of their migration to the spawning grounds (after spawning they die), I don't think infection is a big issue.
All Pacific salmon (which is what these are) die after spawning. A few Atlantic salmon (about 10%, ATW) will survive to make another trip.
The Pacific species basically start to decompose as soon as they hit fresh water.
Once they've spawned, they fall apart like something out of a bad horror movie. I've seen semi-alive fish that you could stick your thumb through without any effort (usually snagged by a tourist who's proud of his accomplishment).
