Fishbones is Jinx's custom-made rocket launcher. Ironically, it is usually the voice of reason and frequently tries to convince Jinx to take the calmer, safer path. Of course, this is only because it is programmed to do so. 

It is a gun. Guns can't really talk.

Fishbones is not required to have a specific kind of voice other than that it sounds slightly robotic, so actors with masculine or feminine voices are all welcome to audition.