the Editor says: Did you know that many creatures on the seafloor only begin to feed and move around at dusk? After the sun sets, the world beneath the waves — once pitch dark — takes on an entirely different character as these animals emerge to mate, spawn, and forage. Next time you head out for a dive, why not give night diving a try! Full article reprinted from: スミレヤッコの繁殖行動を追え！いま、サンセットダイビングがアツイわけ
Why do you dive? If someone asked you that, what would you say? Is it the underwater topography? The thrill of encountering large marine life? The soothing charm of a nudibranch? Or are you simply the kind of person who feels happy and at peace the moment you slip beneath the surface?
The ocean holds a kind of magic — simply slipping beneath the surface is enough to make you feel utterly at ease.
For me, tracking the reproductive behavior of fish is the greatest thrill of all. I believe one of diving's greatest pleasures is observing marine creatures in their unique underwater environment, close enough to almost reach out and touch them.
This series is written by Shota Ishino, a dive guide based in Okinawa, who will introduce some of the fish behaviors that are — shall we say — a little naughty and a lot fascinating. I have no idea how long this series will run, but I hope you'll stick with it until we run out of material.
The Most Exciting Diving Actually Starts at Dusk! Experience the Thrill and a Side of Fish You'd Never See During the Day
Up until now, I think most divers have timed their dive trips around the after-dive drinks that follow. But once the pandemic hit, even gathering in groups became difficult. You'd go to all the trouble of getting out there, only to end up alone in your hotel room scrolling through the day's photos, nursing a solitary drink — a little lonely, all things considered.
In moments like that, why not push back that first drink, and instead plunge into the sea at dusk? In waters that seem calm and quiet after most divers have returned to shore, you can witness fish behaving in ways that are subtly — yet fascinatingly — different from their daytime selves.
The Goatfish, often overlooked during the day, puts on a breathtaking display of color changes when courting.
Males court females with boundless energy, while females focus intently on readying themselves. The entire ocean buzzes with a restless, electric atmosphere.
Of course, some species do engage in reproductive behavior during the bright midday hours. But what you witness at dusk carries with it something extra — a sense of transgression that comes from diving when no one else is in the water, combined with the growing urgency as the light fades. It's genuinely thrilling.
Sunset diving is especially recommended for marine life enthusiasts. Even if you're skeptical at first, give it a try — you might just find that "cracking open a beer the moment I'm out of the water" is no longer your first thought.
As the sky burns red with the setting sun, dive into the excitement of a twilight dive!
Want to Watch the Flame Angelfish Spawn? Find the Suspicious-Looking Male!
The first installment of "Heart-Fluttering at Dusk" focuses on the spawning behavior of the Flame Angelfish.
Flame Angelfish spawning behavior
In Japan, there is a small species of angelfish (family Pomacanthidae) with brilliant blue and yellow coloration, distributed primarily along the Pacific-facing southern coast and the Ryukyu Islands. Around Okinawa, these fish are commonly found in shadowy spots — crevices along steep walls or tucked beneath overhanging reef formations.
They are timid by nature. If you want to observe them during the day, you must approach with extreme care. Shine a bright light on them and they'll vanish into a crack instantly. Despite their stunning colors, they're not especially popular among divers — perhaps precisely because they're so difficult to observe.
At dusk, however, Flame Angelfish become remarkably easy to spot as they move freely around the base of the reef. If you notice a larger individual roaming over a wide area, that's your male!
The male Flame Angelfish has a larger yellow area than the female, and the blue lines on its fins are more vivid.
In the world of the Flame Angelfish, a polygynous harem system prevails. A single male typically maintains a territory shared with 3 to 4 resident females. As the sun begins to set, the male becomes noticeably more active, patrolling his territory and checking in on each female.
If you want to witness spawning, locating the male is absolutely critical. After that, simply follow him — and with a bit of luck, you may get to watch multiple spawning events in a single dive.
A female Flame Angelfish just before spawning — her belly is packed full of eggs!
Is Caressing a Tactic? The Captivating World of Spawning Behavior!
Flame Angelfish reproduce via external fertilization. The pair rises together toward the surface to spawn. As the two fish ascend, the female releases buoyant eggs and the male simultaneously releases sperm over them. The entire act happens in an instant — immediately after releasing their gametes, both fish dart back into the reef, and the fertilized eggs disperse rapidly. If you're not familiar with the behavior, you might not even know what just happened, so keep your eyes sharp and your attention focused.
The fertilized eggs disperse rapidly.
For me, the most remarkable part of this entire sequence is a behavior known as "egg nudging" — an act performed by the male to encourage the female to spawn. It's typically described as "the male gently prodding the female's abdomen." When this behavior appears, it's a signal that spawning is imminent, making it the perfect moment to capture a great shot.
Egg nudging — the male gently prods the female's "belly" during the upward ascent.
It's a little awkward to say out loud, but this behavior strikes me as remarkably tender — almost like the male caressing the female — and it's the moment I find most exciting when watching angelfish spawn. I hope you'll have the chance to witness egg nudging for yourself, but it's far from the only highlight of fish reproductive behavior.
The courtship exchange between male and female before spawning is equally fascinating. As with many fish species, the female has the final say in the Flame Angelfish's reproductive process. No matter how persistently the male courts her, if she isn't ready, he simply has to wait.
Timid females frequently give up halfway through the ascent and retreat back into the reef. Even so, the male must keep courting — he cannot give up. At that point, the observation of spawning is just one small step away! Over many hours of observation, I've witnessed countless false starts; the male only earns his chance to mate once the female is truly ready. This struggle resonates deeply with observers — especially the men in the audience — because there's something both brave and endearing about a male who keeps trying despite repeated rejection.
Just before spawning, the female's belly is so full of eggs it looks ready to burst. Even in this state, she may turn and flee at any moment.
At first glance it may seem as though the female holds all the power in the mating process — but the reality is far more complex than that. The harem contains multiple females, and as night falls, Flame Angelfish retreat into reef crevices to sleep. This means the male must race to complete spawning with every female in his harem before darkness sets in. If he devotes all his time to courting just one female, he won't make it through his full round. If a female becomes difficult, the male may lose patience and move on to the next; if she's also uncooperative, he moves on again. If none of them cooperate, he circles back to the beginning and starts over. Males operate on a strict schedule, and sometimes you'll see a female chasing after a male as if to say, "Wait! Next time, I promise!" — but once he's made up his mind to move on, he won't look back. Within their limited window of time, they play out an intricate, surprisingly strategic game of give and take.
A strong male holds multiple females within his territory.
Each female spawns only once per day, so the moment she's done, the male immediately moves on to the next. Once every female in the territory has spawned, the male — who was buzzing with energy just moments before — instantly deflates and vanishes from sight. One might call this his "sage mode." He retreats with a look of quiet contentment and goes to sleep.
After releasing their gametes, the pair separates immediately. The male wastes no time seeking out his next female.
Spawning Behavior Changes with the Seasons
I've always believed that diving becomes far more rewarding when you return repeatedly to a familiar stretch of ocean and follow the same subjects over time. When it comes to fish reproductive behavior, I'd argue that if you walk away satisfied after capturing just one great photo, you've barely scratched the surface of what this experience has to offer. You only truly appreciate the full richness of spawning observation when you can feel the shift that comes with each changing season.
In spring, for instance, when the breeding season is just getting underway, young females are still unaccustomed to spawning and remain highly skittish. They'll respond to the male's courtship, but you'll often see a nervous female abandon the ascent midway and retreat — much to the male's frustration.
Here's a story that actually happened: I was watching what I was certain was about to become a full spawning event, when another fish happened to swim past at the critical moment. The female froze — but the male, already too worked up to stop himself, released his sperm anyway. He then went scrambling after the female in a fluster, looking for all the world as if he were muttering, "Oh no, that was embarrassing!"
Interestingly, as working styles evolve — remote work, workations, and the like — it may become much easier to slip in a dive after hours or sneak a sunset dive during a week-long business trip. That said, I know many people still find that kind of flexibility difficult to come by. So my hope is that through this humble series, I can bring even a little of the wonder of fish reproductive behavior to your screen — and if it brings you even a moment of joy, I'll be very happy indeed.
These tiny, heart-shaped fruits of love will drift away on the current, embarking on a long and wondrous journey.
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