(CNN) Animal rights groups in Japan have raised the alarm over a dolphin, 46 penguins and hundreds of fish and reptiles that are locked in an aquarium that has been closed for months.

The bottle-nosed dolphin, known as Honey, is being kept on her own in a small pool and is showing signs of mental stress, activists say.

The Inubosaki Marine Park, in the city of Choshi, just east of Tokyo, shut down in January because of a lack of visitors.

Park staff continue to feed the marine life at the aquarium.

But with no companions, Honey -- who was captured from the wild in 2005 -- is condemned to a lonely existence.

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