Phantom tetras are social creatures that prefer to stay in groups. They’re not a schooling species, but they are shoaling fish that will stick together most of the time.
For the most part, this species is non-aggressive. However, males can exhibit some territorial behavior from time to time. The fish often develop a social hierarchy within the group. Males that creep into another’s space may have to answer to a mock fight!
During a mock fight, males will act aggressively towards one another. They may also mirror movements and swim in unison. It’s quite an interesting display.
Luckily, mock fighting usually doesn’t result in injury.