Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Posts: 11,721
Male Bettas may be all aggression against their own or closely related species (other Anabantoids) but their fancy fins makes them slow moving, and a target for other species known to nip fins. I did not know that Roselines were particularly nippy, but I could easily see that they could beat a Betta in a fight. Fast, agile... compared to a fish 'tripping over his own skirts'.