I'll be honest. When this story first started bouncing around the Twitterverse, I was skeptical: Nobody had ever seen this behavior or these structures before? Where is the video? Who are the scientists? Is there any kind of peer reviewed study being written? Was this a hoax? (I wasn't the only one to be dubious; although, inevitably some folks' skepticism had more to do with the this-has-nothing-to-do-with-UFOs explanation.)
My brother, who lives in Japan, checked the links in the original post and assured me that none of them said "Ha, you've been Rick Rolled" in Japanese. I checked with a couple of researchers, who responded with the scientific equivalent of "WTF?" (in fact, one of them did actually type, "WTF"). But I haven't seen or heard anyone blow it up yet.
And if it is true – well, it would be fantastic and wonderful and impressive. But then the natural world frequently astonishes and amazes, particularly when sex is involved. As Jerry Coyne notes in his "Why Evolution Is Real" blog, "sexual selection is a marvelous thing." It leads to behaviors like the singing of humpback whales, physical attributes like the plumage of birds-of-paradise; and the building of extraordinarily elaborate structures, like those constructed by the bower birds of Australia and New Guinea – and, it seems, by tiny fish off the coast of Japan.
Photograph by Yoji Ookata/NHK, via Spoon and Tamago