I can't imagine finding anything regarding a study of fish behavior, but if you do please share a link if it's on the net!

We could speculate all day, but I do know that in a purse seine, where the mesh is small and the thread coarse, fish will avoid running right into the mesh unless they get spooked. They'll mill around and eventually start running up and down the length looking for a way out.

I would imagine that in a river, if they don't see the mesh, they'd pour on the juice as soon as they felt something and that would be the end of 'em. If they see it they'd probably try to go around it, but at top speed, which just increases the chance they'll run into it somewhere else.