The world's loneliest fish has been given cardboard cutouts of people to help ease its boredom.

Caretakers said the sunfish suddenly stopped eating jellyfish and rubbed its body against the glass of its tank after Kaikyokan Aquarium closed down and started its renovation in Shimonoseki, Japan, last month.

They first suspected the marine creature was suffering from digestive issues and parasites, but one of the staff members suggested the behaviour was a symptom of severe loneliness.

To entertain the fish, the park cut out pictures with human faces and glued them over uniforms.

The standees were then displayed outside the acrylic tank to resemble caretakers looking at the fish.

Footage shows the sunfish swimming around its shelter while a visitor watches from the outside. A picture showed how cardboard cutouts were put outside the glass so the sunfish would not feel alone.

Staff member Mai Kato, 26, said: 'The sunfish is popular among visitors. It was always curious and swam up to greet visitors.'

The aquarium closed on December 1 to renovate but will soon reopen in summer, around June to August.

Mai added: 'I hope many people take interest in the sunfish, and when the renovation work is finished, I'd like visitors to wave to it in front of the tank.'

The sunfish arrived at the Kaikyokan Aquarium in February last year where it has been living ever since.

The ocean sunfish is one of the largest bony fish in the world, known for its distinctive, flattened, oval shape and small, rounded tail.