The Trouser Troops are a group of three fish who only appear in the episode "SpongeBob LongPants."
There are three members of the Trouser Troops that all wear the same suit but in different colors. One of them is a green fish wearing a hat with a red stripe on it and a red tie. Another is a taller, light purple fish whose hat stripe and tie are green in color. The third and final fish seen is blue in color whose hat stripe and tie is dark red in color.
Role in episode
They are seen after the salesfish mentions to SpongeBob that he needs to join them, meaning wear long pants like they do. This may mean that SpongeBob looked up to them, as they were presumably one of the prevailing factors to his purchase of the pants.