You can google it for the exact definition but its typically a peaceful fish, like a schooling fish. The idea is having them in the tank mixes up the fish in the tank, encouraging shy fish to explore more and distracting/derailing more aggressive fish. The reason I ask is because they would increase the bio load on the tank, and once your fish grow up, theyre going to out grow your current tank. Adding dithers would make you need a new tank sooner, but if aggression becomes a problem they may help (not a certainty). Just something to think about