A solitary sunfish at an aquarium in southwestern Japan lost its appetite, began banging into the side of the fishtank and appeared unwell days after the facility closed last month for renovations.

SHIMONOSEKI, Yamaguchi Prefecture--A sociable ocean sunfish that clearly missed its human audience and fell sick during renovations perked up after officials set up human cutouts at its aquarium here.

This may sound like the start of a particularly silly joke, but it was a very real challenge faced by staff at a Japanese aquarium when they noticed their sunfish was ailing. Almost as soon as the ...