Something fishy

Yoji Okato pulled on his dive gear. The underwater photographer gathered his waterproof cameras. Then he dove into the sea off southern Japan. 

When he reached the seafloor, he saw something odd. It was a giant circle in the sand. The sand in the center looked smooth. A pattern of ridges was piled up around the edge of the circle. Other divers said they’d seen these mysterious circles, too. Yet no one had ever seen what made them. 

for a Cause

People came up with theories to explain the circles. Some thought they were caused by ocean currents. Others said maybe a UFO had landed on the seafloor!

Okato wanted to solve this mystery. He teamed up with some scientists and filmmakers. The team returned to the spot where he had seen the circle many times. They watched, but didn’t get any clues. The sand circles remained a mystery.

Yoji Okato

sand circle



A pufferfish moves sand as it flaps its fins and swims along the seafloor.

Mystery Solved   

Finally, the team caught the artist in the act. It was a small male pufferfish.

The little fish made tiny waves by swimming back and forth. The waves made a circle of sand. He used his fins to dig dips and build ridges in the sand circle. He collected bits of shell in his mouth. He placed them on the ridges. It took him a week to finish his work.

Okato’s team also learned why the male pufferfish built this circle. He’s trying to get the attention of a female pufferfish. His efforts worked. She laid her eggs inside the circle.

Okato’s patience paid off. The mystery of the sand circle was finally solved. The circle was a nest.

A pufferfish swims back and forth as it makes a sand circle.