An electric eel at the Squa Toto Gifu aquarium in Japan is powering the lights on a Christmas tree. When the eel brushes against a copper electrode in the tan, the current is transmitted to the tree lights. The best part of the Mainichi Daily News article is this nugget:
Officials expect the "eel Christmas tree" to be a popular attraction for dating couples in the lead-up to Christmas Day, when the tree will be removed.
Link (Thanks, Paul Saffo!)