BOISE, Idaho — There is a way to end a population that does not involve a poison, a predator, or a drought. It involves, instead, a single very confident fish.

Fisheries biologists have been quietly perfecting a technique so elegant that it has inspired a nickname — the breeding of “supermales,” genetically modified males who, when released into a lake, mate with every available female and produce nothing but sons. No daughters. No next generation. The population, deprived of mothers, simply stops. It is, in the words of one researcher, “a sex-ratio nuke,” and it has, as of this year, been shown to work on the wild, according to FishBio’s account of the technique.

The target is the brook trout, a fish that is, depending on whom you ask, either a beloved native or a relentless invader. In the lakes where it has no business being, the brook trout is a menace — outcompeting native species, eating their young, and generally conducting itself with the quiet arrogance of a creature that has never once been told no. The supermale, in this telling, is the answer: a male so aggressively male that he tips the entire lake toward a future in which there is no one left to lay eggs.

"We're not killing the fish," the researcher said. "We're just making sure the fish can't have any."

The science is older than the nickname. The technique has been tested in the wild in Idaho since 2014, and the principle — flooding a population with males until females become a statistical rarity and then a biological impossibility — has been studied in laboratories for decades. What makes the current moment interesting is not the method but its maturity: the question has shifted from “can it work” to “how many do we drop, and how long before the lake goes quiet.”

THE SUPERMALE, DEBRIEFED

  • What it is: A male fish, engineered to sire only sons
  • How it works: Flood the lake with males; females run out
  • Result: No daughters, no next generation
  • Target: Invasive brook trout
  • Timeline to silence: A question for the biologists

There is a grim poetry to it that the researchers, to their credit, do not shy from. The supermale is a fish whose entire existence is a service to the extinction of his own kind. He is, in a sense, the most selfless creature in the lake — a being whose love, if it could be called love, is so total that it leaves nothing behind. The native fish, for their part, do not know they are being saved. They simply notice, year by year, that the brook trout is a little less common, a little less loud, a little less certain of its place.

At press time, the biologists were finalizing the count — how many supermales it takes to quiet a lake the size of a lake — and, as one of them put it, “we’re not in a hurry. The fish aren’t going anywhere. That’s rather the point.”