It was Mr. Noguchi who, over eight years, conducted a study underpinning what two decades of fish farming in Japan had already shown: that fugu could be made poison-free by strictly controlling its feed.
Decades earlier, another Japanese scientist had identified fugu’s poison as tetrodotoxin, a neurotoxin that leaves victims mentally aware while they suffer paralysis and, in the worst cases, die of heart failure or suffocation. There is no known antidote.
Researchers surmised that fugu probably got the toxin by eating other animals that carried tetrodotoxin-laden bacteria, developing immunity over time — though scientists then did not rule out the possibility that fugu produced the toxin on its own.
By this year, Mr. Noguchi had tested more than 7,000 fugu in seven prefectures in Japan that had been given only feed free of the tetrodotoxin-laden bacteria. Not one was poisonous.
“When it wasn’t known where fugu’s poison came from, the mystery made for better conversation,” Mr. Noguchi said. “So, in effect, we took the romance out of fugu.”
I'm guessing if they released non-poisonous fugu back into the wild, they would go back to eating the same bacteria that creates tetrodotoxin. It probably serves as protection of sorts, against being eaten.