Actually, eels can produce a shock as great as 600 Volts.
An electric eel (Electrophorus electricus) has electric-current-producing organs within plates located on both sides of its spinal column. The plates run almost its entire body length.
The electric eel's charge—which is 350 volts on the average but may be as great as 550 volts—is released by its central nervous system. The shock consists of four to eight separate charges, which last only two- to three-thousandths of a second each. Used as a defense mechanism, the shocks can be repeated up to 150 times per hour without the eel tiring. The most powerful electric eel, found in the rivers of Brazil, Colombia, Venezuela, and Peru, produces a shock of 400 to 650 volts.
Sources: Grzimek's Animal Life Encyclopedia, vol. 4, pp. 296-297; The Guinness Book of Records 1996 p. 35; Taber, Robert W. 1001 Questions Answered About the Oceans and Oceanography, p. 143.