How do you kill a convict?

[Fish on Fire]

A hungry catfish, leaving them out of water, freezing them, good old blunt force, big male dovii, etc. Lots of ways to kill a convict.

 

[mudangel]

Nuke 'em from orbit, it's the only way to be sure...

 

[yonderway]

Convicts are freshwater cockroaches.

Scorpionfish are the saltwater variety (long story from my LFS days in the 1980's, and I'm sure I'll get the details of it wrong).