The betta fish (more specifically the B. splendens variety) are often known as the world’s worst underwater room-mates. Males will immediately try to attack one another, or attempt to hurt their own reflection in a mirror. Because of this they are better kept in separate tanks, though some live with different and larger breeds of fish that don’t pose as a visual threat to a betta. Males don’t usually attack females on first sight, but after mating they have been known to battle each other.