There are more electrogenic fish than is usually realized. Few pack the high voltage punch of the 'electric eel' Electrophorus electricus, but there are other and not uncommon electrogenic knifefish and catfish. The African elephant nose which is commonly available in the trade is a good example.
Most if not all seem to be FW fish and use their electric organs for prey detection or defense/attack in turbid and low visibility water.
Now if you kept a big Amazonian 'electric eel' in a species tank, maybe you could use him as emergency backup during power outages :mrgreen:
PS. The ugly bugger that the three guys are holding is a Wels or European giant catfish. They are native to the Danube and rivers and lakes of Eastern Europe, but anglers have irresponsibly introduced them to waters elsewhere.