Wow! I love the way your mind is always roaring along at full speed. Danged good question!
My guess (and that’s all it is) would be that they will behave as though it is dusk, followed by night, followed by dawn all within a couple of hours, particularly in the area of the full eclipse. So, good fishing, I’d say. Now you got me thinking I need to be on the stream during the eclipse. I’m nowhere near the zone that will experience the full eclipse, but it would be fascinating to see how the fish react.