There are venomous fish!
The world’s most venomous fish (not to be confused with the most poisonous fish) is the Synanceia or Stonefish. The stonefish is a fish with sharp fins that can pierce skin and deliver a deadly venom. Stonefish stings are painful, cause swelling, and sometimes they require amputations if not treated quickly enough. A large enough dosage of the venom can even kill someone.
Stonefish get their name because they look like stones. People have stepped on them without even noticing them. This is bad, because they can sting through your shoes.