Hello everyone, I'm photographer Ishino. "Japan Underwater Odyssey" is a series that follows the turning of the seasons, visiting dive sites across Japan to capture the faces of marine life that can only be encountered in specific seasons and specific places.
June is the calmest time of year in Japan's waters. As the water temperature gradually rises, the sea welcomes conditions ideal for fish reproduction. This time, I left the main island of Okinawa — deep in its rainy season — and headed to Amami Oshima, located between Japan's main island and Okinawa. In these waters, rich in natural resources and home to a unique ecosystem, I witnessed a magical and unforgettable courtship behavior.
The star of this piece is the Amami Hoshizora Puffer (Torquigener albomaculosus), a small pufferfish found only in the waters surrounding Amami Oshima.
A Tiny Star of Amami Oshima
The Amami Hoshizora Puffer measures only about 10 cm in length. The first time I encountered one underwater, the impact it had on me far exceeded what its small size might suggest.
Why can such a little fish be so captivating? The answer lies in its extraordinarily unique and delicate reproductive behavior.
Around 2015, I first heard of this fish. The species wasn't formally recognized as a new species until 2014, and what truly captured global attention was the astonishing structure that males construct during the breeding season: a massive circular nest on the sandy seafloor.
Geometric Art on the Sand
Once the breeding season begins, male Amami Hoshizora Puffers select a patch of sandy seafloor with good water flow and start constructing a circular nest that can reach up to 2 metres in diameter. Viewed from above, these nests display precise and breathtaking geometric patterns that are almost impossible to believe.
At first glance, they look like the product of deliberate human artistry — yet these patterns are far more than decorative.
The outer ring of the circle is carved with radiating ridges, while the center is slightly depressed, creating an area of relatively calm water flow. This structure is thought to prevent eggs from being swept away by strong currents — a remarkably rational, highly functional design.
That a fish barely 10 cm long would spend nearly a week building a structure dozens of times larger than its own body is, in itself, deeply moving.
A Display of Life Through Nest-Building
Not every male succeeds in reproducing. The quality of the nest plays a decisive role in whether a female is attracted to lay her eggs there.
As a result, males invest enormous effort into construction. To make the nest more appealing, they carefully arrange small shells and coral fragments, as if adding the finishing touches to a work of art.
As the nest nears completion, the male continuously fine-tunes the central area until it reaches the ideal state — only then is the nest truly finished.
Only when a female approves of the nest and draws near does the chance to reproduce finally arrive.
A Quiet Waltz at the Heart of the Nest
Once the female enters the nest and begins to spawn, the pair moves close together at the center of the circle — slowly, gracefully, like a silent waltz.
On the sand, life is gently and carefully entrusted to the next generation. It is not a showy spectacle, yet it is one of those rare moments that is both beautiful and utterly fleeting.
Nearby, however, I also saw nests that had never attracted a single female — abandoned structures that, as time passed, gradually blurred and faded, eventually returning to the sand. They spoke in silence of the harsh reality that accompanies this reproductive strategy.
What Divers Need to Know and Be Capable of as Observers
During the breeding season, the Amami Hoshizora Puffer becomes especially sensitive and alert. If a diver approaches too suddenly, or stirs up silt near the nest, the male may abandon the nest entirely and cease all reproductive behavior.
Once a nest is abandoned, it will never be used again. For that male, it could mean losing what may be the only opportunity of a lifetime.
Observing this phenomenon therefore requires solid neutral buoyancy control and a deep respect for the ocean. Avoiding silt disturbance, maintaining an appropriate distance, and keeping movements steady are all non-negotiable — and these behaviors are, in practice, a vital way of protecting the fragile thread of life unfolding before your eyes.
A Love Story for Survival in the Waters of Amami Oshima
The waters around Amami Oshima possess a quiet depth quite unlike the experience of large pelagic fish schools or vibrant coral reefs. The nest-building and courtship of the Amami Hoshizora Puffer is a perfect symbol of this sea's subtle richness.
This spectacle — visible only in early summer, only at Amami Oshima — is precious not merely for its rarity, but because it is a drama of life that plays out briefly, in a specific time and place, and nowhere else.
If you wish to truly feel the depth and layered richness of the ocean, I invite you to visit the waters of Amami Oshima in early summer.
The geometric nests drawn upon the sand, the love story woven by these tiny pufferfish — it is a memory that will stay with you for a lifetime.
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