Which fish creates elaborate geometric sand circles on the seafloor to attract mates?

The white-spotted pufferfish creates elaborate geometric sand circles on the seafloor to attract mates. A male uses his fins and body to sculpt ridges, grooves, and a maze-like center, producing an intricate nest that signals his courtship effort to females.

The circles are built in sandy marine habitats around Japan’s Ryukyu Islands. Each structure can reach about two meters across, even though the fish itself is only around 10 centimeters long. Construction takes roughly seven to nine days, and the male continually maintains the design until spawning.

Divers first noticed the mysterious circles in 1995, but their maker was not identified until observations in the early 2010s. The behavior became famous because the patterns look almost engineered, with carefully arranged valleys and peaks that concentrate fine sand in the center. Females inspect the structures and may lay eggs in the selected nest; the male then guards them until they hatch.

The pufferfish does not reuse the circle after spawning. Similar structures have since been reported in Australia, although researchers are not certain which Torquigener species builds them, so the white-spotted pufferfish remains the canonical answer for the Japanese “mystery circles.”