For details on spawning behavior, see Brook Trout Spawning.
Video (scroll down) shot last October follows below of the steady-state behavior.
I don’t actually know which fish is the female and which is the male, but only the smaller fish in front engaged periodically in this flip-flop behavior, which I presume is a mechanical aid in releasing eggs (or sperm).
Watch a larger video of these brook trout. Regrettably I did not catch them in full action as above, but the video shows the typical steady state behavior. Crappy YouTube kills the 1080p quality, sorry. The annoying background noise is the Leica M Typ 240—how can anyone do video with that kind of camera-induced noise?
Photographer Tom Kline has some spawning shots underwater.