Thousands of glass and plastic bottles lie across the floor of Tran Ngoc Thang's farm in Hanoi, each one home to an aggressive, brightly coloured fish that must be raised alone.
Thang has been breeding Siamese fighting fish, also known as betta fish, for more than 20 years in Vietnam — and his business is going swimmingly.
They were once prized for their combative nature and were pitted against each other in fights, with bets placed on which fish would triumph.
Now they are mostly kept for ornamental purposes but are still kept apart on Thang's fish farm to avoid any clashes.
"I have studied the character of these fighting fish, and I know used plastic bottles are a good place to raise them," he told AFP, explaining that he collects bottles from the local train station.
"I cut the bottle neck, and drill a hole, which makes it easier when I want to change the water," the 54-year-old said, adding that the fish are fed everyday from a nearby pond.
This way, "caring for them is much easier and we can avoid them fighting each other".
On top of other fish species, Thang raises around 3,000-4,000 betta fish a year, and sells them for between 50 cents and $5 each.
One of his clients, 35-year-old Bui Doan Tung, has been devotedly buying all kinds of Siamese fighting fish — halfmoon, dumbo, fancy and koi — for the last four years.
"They are not for fighting now, just for admiring," he says. "Each type is beautiful in a different way."