The electric eel is famous for producing a strong electric discharge with specialized organs.
Despite its common name, the electric eel is not a true eel. It is a knifefish from South America and breathes air, surfacing regularly. Its electric organs are derived from modified muscle cells called electrocytes. When many electrocytes discharge together, they create an electrical pulse.
Electric eels use weaker electrical signals for sensing their surroundings and stronger discharges for hunting or defense. The electric eel Electrophorus voltai has been measured producing voltages of up to about 860 volts, although output depends on the species, the individual, and the conditions.
Electric rays also generate electricity, so the answer is not unique if a question merely asks for an animal that can shock prey. The electric eel is the standard answer when the question specifically refers to the famous South American freshwater fish and its powerful discharge.