I have one of those. They are commonly called black cap jawfish or tiger jawfish. They require a tight fitting lid, as they are jumpers. The one I have is a perminant resident of my refugium. He kept jumping into my overflow, so I just left him down there. Since he's been down there I haven't seen it try to jump. They are also carnivores, and in some cases you have to make sure that you get the food by there den. They can be kinda touchy. They don't do well with others of their own kind often times fighting to the death. HTH