From March onward, ocean-opening events are held across Okinawa Prefecture, and you can gradually start to see people swimming and playing in the sea. By April, the water temperature rises to 23°C, and fish activity picks up considerably. Night diving in a wetsuit still feels a bit chilly this time of year, but these days you can slowly start to sense that summer is on its way!
In my previous article, "The Thrilling Moments of Dusk," 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 topic of this second one — and yes, you're right! It's the Goatfish (family Mullidae)! This species belongs to the family Mullidae and is widely distributed in Japan, ranging from the Pacific side of southern Japan all the way to the Ryukyu Islands. This time, we'll be observing the spawning behavior of the goatfish during a night dive.
You may have had this experience before — a dive instructor points to a school of small fish and jokes, "These are baby goatfish, you know (laughs)" or "This one is a female goatfish ♀." Maybe I'm the only dive instructor who makes that kind of joke, but it's surprisingly well-received. But back to the main topic: you've surely watched with great interest as a goatfish skillfully manipulates its two barbels to forage along the seabed. You might not pay much attention to this common fish anymore, but in fact these ubiquitous, ordinary species are the very best subjects for behavioral observation. Take my word for it — give the goatfish another look!
If you observe the goatfish for an extended period, you'll notice that their body color sometimes turns red.
The goatfish — a familiar, everyday species.
Pay Attention to the Goatfish's Barbels
The species we're observing this time — the goatfish — is known in Japan as "Ojisan (オジサン)", while in Taiwan it's commonly called a "goatfish." Whether it's a young individual or an older female, it's still called Ojisan — no matter what, this fish goes by the name Ojisan. The name comes from the two barbels dangling beneath its snout, which serve as its sensory (taste) organs, allowing it to probe through sand in search of hidden crustaceans and other prey.
A goatfish in the middle of foraging.
When you watch a goatfish closely, you'll see it moving slowly across the rocky surface, then suddenly bursting forward when a small fish darts out from a crevice. The two barbels beneath its snout are critically important during foraging — but when observing their spawning behavior, pay special attention to those barbels, because during the breeding season, the goatfish puts them to use in a move that might just make you blush.
The Cool, Territory-Defending Goatfish
Before we get to the barbels, let's first take a look at how goatfish spawn. Like the Flame Angelfish, goatfish spawn in pairs. The pelagic eggs they release drift freely in the water column. During spawning, the male and female rise together into the water column to release their eggs and sperm — quite unlike their usual image of creeping along the sandy seabed or reef. They ascend together to an almost unimaginable height to spawn.
A pair of goatfish ascending together to spawn.
It's difficult to tell males from females by appearance alone, and group size is hard to gauge. However, toward evening, you can see them gathering around particular rocks, with the dominant male forming a loose harem of females around him. The reason I say "loose" is that you occasionally see spawning taking place outside the group, which suggests the boundaries of the harem are quite fluid.
Even so, the dominant male still wants to spawn with as many females as possible. In the reef area I frequently observe, this dominant male will instantly charge at any intruding male that dares approach his harem — so fast that you can sometimes almost hear a whooshing sound. No matter what he was doing before, the moment he spots an intruder, he tucks in his barbels and fins to minimize drag and launches an explosive pursuit, defending his harem without mercy.
When swimming at high speed, the goatfish tucks in its fins and barbels.
The sight of the goatfish spawning so magnificently within its own territory is just incredibly cool! Goatfish are awesome! As for the individuals mentioned earlier that spawn outside the main group — they've probably lost out to the dominant male and are sneaking off for a secret rendezvous on the side. It's a little sad, really.
A male goatfish choosing among the females in his harem.
The Goatfish's Barbels Pull Off a Strange Move
Just by anthropomorphizing the rivalry between the sneaky suitors and the No. 1 male, the spawning process of the goatfish becomes endlessly entertaining. But there's one more thing you absolutely cannot forget — the barbels! You simply cannot talk about goatfish courtship and spawning without mentioning the barbels. I think the most spectacular part of goatfish reproduction is the barbel display during courtship. Those barbels, ordinarily used for foraging, take on an entirely different role when it comes to winning over a mate.
The normally plain-looking goatfish transforms during courtship, its body shifting to a purplish hue so striking that you'd almost think it was a completely different species. The male, dressed in his vibrant nuptial coloration, erects his dorsal fin as high as it will go and swims directly in front of the female — and then, in the next instant, vibrates his barbels at blindingly high speed in an utterly mesmerizing display.
A beautiful goatfish in nuptial coloration.
If I had to put the scene into words, the Japanese onomatopoeia "berobero" fits perfectly — imagine that comedy sketch where someone licks an idol's toothbrush. It's a little gross, honestly. This bizarre courtship technique is unlike anything you'd see in other fish.
A courting male goatfish ♂ and a receptive female ♀.
Those goatfish pouring their hearts into courtship, giving it absolutely everything they've got. Some of you might feel a touch of revulsion — but do you know that feeling of wanting to look at something disturbing, or more precisely, covering your eyes and peeking through your fingers anyway? That high-speed barbel waggling is burned into the back of my eyelids and just won't go away.
Ah, I think that qualifies as a kind of trauma.
The passionate courtship of the goatfish plays out every single night.
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