Help! Fish finder interpretation

[Joe_Dizzy]

Hoping some of you would be willing to shed some light on what I am seeing on my garmin striker 4 fish finder.





This is with the 200hz signal and the screen scroll set to auto. 

I get these diagonal lines or slashes. I have yet to see a defined “arch” on the screen. The bottom readings feel like they are accurate only cause I can see bowls, humps, sunken logs, and I think bushes. But I am not sure what to make of these diagonal lines.
I would appreciate any feedback. This is my first fish finder mounted on a float tube.

Those diagonal lines are fish rising up off the bottom. Likely snatching chironomid pupa that are starting their ascent to the surface. 

I have a Garmin on my tube (kicking/rowing) and see these all the time when targeting trout. It's exactly the kind of activity I'm looking for when hanging a chironomid imitation off of an indicator.

Suspended fish (on a slow-moving watercraft) show as horizontal lines across the screen.