beta fish

noun2

1. •
   Betta.

   • His chest puffed out like one of those Japanese beta fishes when it had caught a glimpse of itself in a mirror. — 2009
2. •
   A person who is in a secondary position in a social hierarchy; a submissive person; a follower.

   • And beta fish can't be beta fish if they are fighting to be alpha fish. — 2017