Looking at this male Asian sheepshead wrasse, you might not guess that he started his life as a pouty-lipped orange whip of a baby. You may also be surprised to learn that he began life as a female.

These beginnings are common to most wrasses, a diverse group of colorful marine fishes found in temperate and tropical waters. The Asian sheepshead species (Semicossyphus reticulatus), or kobudai in Japanese, is among the largest of the group, and makes its home in rocky reefs and wrecks around Japan, Korea, and off the coast of China. As each individual grows, she begins to change color and sprout a distinctive hump just above her eyes. If she is among the strongest and largest of her kind by around 10 years of age, she may begin a months-long transformation, her chin elongating below her jutting snaggle teeth and her forehead expanding further as she becomes male. It’s unclear what triggers this sex change, but for the bluehead wrasse (Thalassoma bifasciatum), at least, scientists believe it’s caused when the largest local female senses the absence of the dominant male, which may release a cascade of stress hormones that initiate her transformation.

“You look at [the sheepshead wrasse] and go, ‘Oh my god, what is this thing!” says photographer and naturalist Tony Wu, who has described the fish’s appearance as its “ugly superpower.” “They’re very charismatic, and like a lot of wrasses and a lot of other big fish, they can be quite interactive.” This one, which Wu photographed during the spring of 2017 off the Japanese island of Sado in Niigata Prefecture, had become accustomed to people and swam alongside Wu as if to say hello. In the Yamagata Prefecture just to the north, another diver, Yoshifumi Aihoshi, has swum with the same individual wrasse for two decades.

That’s not to say the fish are friendly with everyone. Male Asian sheepshead wrasses, which can grow up to 3 feet long and weigh 30 pounds, are territorial, and fight to control harems of females. Should one bulbous behemoth encounter another during the breeding season, Wu says, they both “change color simultaneously, like chameleons”—their white and pink hues intensifying. “When you’re out there and you see them light up, it’s like seeing a neon sign turn on.”

The dance of aggression that can follow is simultaneously measured and mesmerizing. The two males back up, and come together open-mouthed, nearly touching. Then they back up and come together again, as if they’re screaming into one another’s throats. Whoever prevails in this repetitive display by eventually driving the other off with a powerful bite gets to spawn with the territory’s females, a process that involves the pair swiftly swimming and swirling from deep underwater to near the surface.

Photographing the wrasse’s steep reverse spawning dive wasn’t an option for Wu. “Humans should not be shooting from 20 meters up to 5 meters in a few seconds—you’d die of decompression sickness.” And even when the fish wasn’t rapidly ascending, the lighting was tricky because the water is so dark and the fish so light. But after 15 years of planning and working with a friend to design special equipment, Wu managed to capture this striking portrait of a fabulous and fascinating fish.