They ignore you. Since when were you their boss, anyway?
Either way, they do what is natural. They attempt to break through. They're mainly breaking through upwards, looks like.
Pristobrycon draws a knife and starts hacking away. She stabs and kills a pirahna.
Pygocentrus shoots a pirahna, killing it.
Pygopristis knocks a pirahna unconsious with his pipe.
You back off a bit, the pirahnas ahead of you are starting to swarm.
"GO! GO! GO!"
"Lets get out of here!"