The vibrantly-coloured animals, also known as Betta fish, can go for as little as $5 in Thailand, where the species is native.
But highest bidder Chuchat Lekdeangyu said he could not back down from the online price war after seeing the fish's iridescent, patriotic pattern.
"There have been other fighting fish that resemble the national flag before but none with as clear colours as him," said the 44-year-old freelance photographer and fish enthusiast.
"It is a lot of money for me but I think it is worth it," he told AFP, adding that he has named the three-month old fish "Tri-colour" in Thai.
He plans to snap photos of the pet and keep it in its own tank to avoid the territorial death-matches the species is famed for.
"I want to show the world that Thailand can breed a beautiful fish. This one belongs to all Thais," said Chuchat.