Male-male Competition

Trout are very agressive and territorial species. They occupied certain spot for feeding, just like fisherman occupy certain spot/honey hole for fishing! Same thing! Because it is easier to obtain food/fish and save energy to maintain their position. Eddies, obstacles that break the currents, all good spots for holding trout.
Bigger trout have first choice to occupied the better spots. Like your elder lab mates always got the window seat first.
Trout compete for food, also compete for mates in the breeding season. The testosterone fire them up. They can fight all day without eating anything... see salmon spawning. These two guys are guarding the same female in the spawning bed. Of course there is not room for the 3 fish...ever once of a while these two guys will dare into the pool just in front of the spawning bed and start the fight...very interesting to see them display/fight...