Freshwater Stonefish
These are venomous fish, and that is the first thing to know rather than a footnote. The freshwater stonefish carries venom glands at the base of its dorsal spines, and a sting is a medical event, not an inconvenience. It is also a true ambush predator: it sits still on the bottom, disappears against sand, and takes anything that swims within reach of its mouth.
Handle it only with a container, never a hand and never a net you then reach into. Keep the tank species-only or with fish too large to be swallowed, and tell anyone who maintains the tank what is in it. If you are not certain you want a fish you cannot safely reach past, buy something else. Questions before you order go through contact.