Two aluminum panels inside the eel’s tank work as electrodes to catch its power. Cables attached to the panels supply the lights on the nearby tree with electricity.
Inventor Kazuhiko Minawa said it took him more than a month to devise a system that would effectively harness eel power.
"If we could gather all electric eels from all around the world, we would be able to light up an unimaginably giant Christmas tree," Minawa told Reuters Television.
Eels are widely eaten in Japan, especially in the summer, when their vitamin-rich flesh is seen as a way to regain stamina sapped by the heat.
The tree, which will stay illuminated until Christmas, is proving a popular attraction, drawing tourists from all over the country.
"I would love to have an eel like this at home. This is very nature-friendly," said visitor Harumi Yayoi.