Corydoras Killing?

[pangasiusfan]

I read that Corydoras posess a sharp spine that is poisonous and can sting the ones who try to eat it but, thats the only thing it said on the resource...
can they kill other fish that they sting?

These are my cory cats but they're aldofis right?

 

[pangasiusfan]

oh and they're swimming in the middle section very actively right now but are they trying to come up for air? is the fluval 404 too strong or something??
is breathing air a must?