A koi fish seller says business is booming, thanks to his careful attention to detail. He sometimes visits 20 breeders a day to source fish that can sell for thousands.

• Tim Waddington has more than 30 years' experience selling koi carp.
• His Quality Nishikigoi store serves customers from South Africa, Trinidad, and the US, among others.
• He told Insider what it takes to run a profitable koi business.
• See more stories on Insider's business page.

Sourcing and selling koi carp – some of the most expensive pet fish in the world – can be both a profitable business and an enjoyable pursuit. This is especially true for Tim Waddington, the owner of Quality Nishikigoi, which is one of the UK's largest importers of Japanese Koi.

As previously reported by Insider, the most expensive koi fish ever sold was worth $1.8 million.

Originally raised in Japan during the 1700s, koi gradually moved through the rest of the world over the years as people began to take an interest in the vibrant and colourful species.

"My father pioneered bringing Japanese koi to the UK. He opened the first koi-only retail outlet in the '80s," said Waddington. Now, with more than 30 years of experience, Waddington has become an expert in the trade and told Insider about how he runs his rapidly expanding business.

There is consistent demand for koi, according to Waddington. "People are always looking to buy the fish," he said. To capitalize on that demand, Waddington said he provides customers with the highest quality Japanese koi that he sources himself, which are sometimes valued at thousands of dollars.

Some of the fish Waddington sells are priced up to $2,700. But like anything expensive, people are more likely to buy pricey items as a one-off purchase. This is why selling cheaper koi is generally more profitable in the long run, Waddington said.

A higher price can also mean a greater loss, however, because there's a lot of things that can go wrong with fish, Waddington said. "You've got to take losses as some fish may die."

Waddington has had some of the same clients for over 20 years. "I've got clients in South Africa, Trinidad, Dubai, America, and most recently, India. It's very much word of mouth which takes time and experience," he said.

Since Waddington's main business consists of sourcing high-class koi, frequent travel to Japan is essential. He has visited Japan more than 70 times in his career, spending about four weeks there for each trip.

"When I go to Japan, I'm looking for fish for my own shop but I'm also looking for fish for other dealers. I'm also looking for individual fish at certain sizes, ages, and varieties," he said. "I might visit 20 breeders in a day."

He looks for koi with vibrant colours and takes a list with him on trips to find specific koi - perhaps ones with a particular colour or pattern - for customers.

As a result, sellers need to choose koi with prized bloodlines that can only be obtained from selective breeders.

While some may buy koi as a household pet, others purchase the fish to enter them in competitions to name the champion koi, just like in racehorsing, Waddington said.

In fact, one of the fish supplied to a client recently won the South African National Koi Show.

"That's what people want me to do: find them these fish where they can win shows with them or just to appreciate them," Waddington added.