An aquarium in Japan is shocking visitors with its Christmas display -- using an eco-friendly electric eel to illuminate the lights on its holiday tree. Each time the eel moves, two aluminium panels gather enough electricity to light up the 2-metre (6 ft 6 in) tall tree, decked out in white, in glowing intermittent flashes. The aquarium in Kamakura, just south of Tokyo, has featured the electric eel for five years to encourage ecological sensitivity. This year, it added a Santa robot that sings and dances when visitors stomp on a pad. "We first decided to get an electric eel to light up a Christmas tree and its top ornament using its electricity," said Kazuhiko Minawa, on the public relations team for the Enoshima Aquarium. "As electric eels use their muscles when generating a charge, we also thought to get humans to use their muscles to light up parts of the tree and power Santa." Visitor Sumie Chiba was fascinated with the display but questioned the practicality of eel energy for domestic use. "If this was possible, I think it's very nice and extremely eco-friendly," she said.