[Japan | Okinawa Island Diving] The Secret Behind the Banded Goatfish's Lightning-Fast Courtship! Stunning Color Changes — A Spawning Behavior Worth Watching

Starting in March, ocean-opening events are held across Okinawa Prefecture, and you can gradually begin to see people swimming and playing in the sea. By April, the water temperature rises to 23°C, and fish activity intensifies. Although night diving in a wetsuit during this period still feels a little chilly, these past few days have made it easy to sense that summer is just around the corner!

In my previous article, "The Thrilling Twilight Hour," I wrote about the joy of observing the spawning behavior of the Flame Angelfish. Those who read that first installment may have already guessed the subject of this second one — and yes, you're right! It's the Banded Goatfish (goatfish)! This fish belongs to the family Mullidae and is a widely distributed, common species in Japan, ranging from the Pacific-facing southern coast of Japan to the Ryukyu Islands. This time, we'll be observing the spawning behavior of this goatfish during a night dive.

Perhaps everyone has had an experience like this: a dive instructor points to a school of small fish and jokes, "These are juvenile goatfish (laughs)" or "This is a female goatfish ♀." Maybe I'm the only dive instructor who does this, but that kind of joke is surprisingly well-received. Getting back on topic — you've surely watched with great interest as a goatfish skillfully manipulates its two barbels to forage. You might not pay much attention to this common fish anymore, but in fact these ubiquitous, ordinary species are the most suitable subjects for behavioral observation. Just take my word for it, and turn your attention back to the goatfish you've been overlooking!

Pay Attention to the Goatfish's Barbels

The subject of this observation — the Banded Goatfish — is known in Japan as "Ojisan (オジサン)", while in Taiwan it is commonly called a goatfish. Whether the individual is young or an older female, it's still called Ojisan — whatever the case, this fish is called Ojisan. The name comes from the two barbels beneath its snout, which serve as sensory (taste) organs, allowing the fish to search for crustaceans and other prey hiding in sandy substrates.

When you observe the goatfish closely, you'll notice it moves slowly across rock surfaces, then suddenly bursts into a sprint when a small fish darts out from a crevice. The two barbels beneath the snout are critical for foraging, but when observing their spawning behavior, be sure to pay special attention to these barbels as well — because during the breeding season, the goatfish uses them to perform some rather eyebrow-raising moves.

The Dashing Goatfish That Guards Its Territory

Before getting to the barbels, let's first introduce how the goatfish spawns. Like the Flame Angelfish, the goatfish spawns in pairs. The pelagic eggs released drift freely in the water. During spawning, the male and female rise together into the water column to release their eggs and sperm — quite different from their usual image of crawling along sandy or rocky seabeds. They ascend together to heights you'd never expect, then spawn.

It's difficult to distinguish males from females by appearance alone, and group sizes are also hard to gauge. However, toward evening, you can see them gathering on particular rocks, where the strongest male forms a loose harem with several females. The reason I describe it as "loose" is that spawning outside the group can occasionally be observed, suggesting the boundaries of the harem are rather vague.

Even so, the strongest male still wants to spawn with as many females as possible. In the reef area I regularly observe, the dominant male swiftly chases off any rival males that try to approach the harem — so fast that you can sometimes almost hear a "whoosh." No matter what that male was doing beforehand, the moment it spots an intruder, it tucks in its barbels and fins, minimizes drag, and launches a rapid pursuit, defending its harem with zero mercy.

The sight of a goatfish spawning majestically within its own territory is incredibly cool! Goatfish are awesome! As for those goatfish spawning outside the group mentioned above — they've probably been outcompeted by the dominant male and are forced to sneak around for a secret rendezvous. It's a little sad, really.

The Goatfish's Barbels Pull Off a Strange Move

Simply anthropomorphizing the rivalry between the sneaker males and the No. 1 dominant male makes the goatfish's spawning process endlessly entertaining. However, there's one more thing we must not forget — the barbels! You simply cannot talk about goatfish courtship and spawning without them. I believe the most spectacular part of goatfish reproduction lies in the barbel movements during courtship. The same barbels used for foraging take on an entirely different role during mate attraction.

The normally plain-looking goatfish transforms during courtship, its body shifting to a striking purplish hue so beautiful it seems like a completely different species. The male, now dressed in nuptial coloration, erects his dorsal fin as high as it will go and swims in front of the female — then, in the very next instant, vibrates his barbels at ultra-high speed in an irresistibly alluring display.

If I had to describe the scene in words, the onomatopoeia "bero-bero" fits best — imagine the moment when a comedian licks an idol's toothbrush, which is a little gross. This unusual courtship behavior is unlike anything seen in other fish species.

The goatfish pouring its heart into courtship, going all out no matter what. Some of you might even feel a slight twinge of revulsion — but do you know that feeling of wanting to look at something disturbing, or more precisely, peeking at it through the gaps between your fingers while covering your face? That high-speed tongue-like motion is burned into the back of my eyelids and simply won't fade.

Ah, perhaps this counts as a kind of trauma.

Related Links

• Original article: 【オジサンの繁殖行動】超高速秘技！美しく体色が変化したオジサンの求愛に刮目

• 【Japan | Okinawa Island Diving】A Sweet and Heartwarming Love Scene! A Complete Record of the Arc-eye Hawkfish's Spawning Process!

• Author: Shota Ishino