One could say that Mr Pay Bok Sing, owner of Nippon Koi Farm, did it his way when he ventured into rearing seawater food fish in his land-based farm.

From making his own seawater to creating a filtration system, to mixing the fish feed, everything is self-made. Mr Pay decided to diversify when his ornamental fish farm was hit by the koi herpes virus in 2010, which wiped out thousands of his fish. "That was when I thought I probably should diversify," he said, adding that it was also around the time when profits from koi started to fall. "So I started studying how to rear food fish."

Mr Pay visited kelongs but realised that they were vulnerable to plankton blooms. So he decided that it was safer to rear food fish in his land-based farm.

He has since invested $400,000 in his new venture.

Armed with information from online research, the 53-year-old invented a seawater recycling system for each of the roughly 100 tanks now being used to rear food fish at his Neo Tiew Crescent farm.

He then bought barrels of minerals, including magnesium and calcium, and started mixing them to make seawater.

But when the fish were put into the seawater he created, some started to act like "zombies", Mr Pay said in Mandarin, explaining that they moved very slowly and seemed to be in a state of stupor. Others became ill, he added.

"We would monitor the (fish) and change the mix," he said.

It took numerous attempts over two months to get the mix right, which he described as "hitting the jackpot". Thereafter, he started producing the secret concoction in large volumes. His fish feed is also a self-made formula that includes fish meal, spirulina and flour.

His tank system - which filters, oxygenates and cleans seawater in three-hour cycles - allows the farm to rear 500 prawns per sq m of water. That is more than five times the amount compared with a similar-sized cage in the sea without such a system. It also lets him rear three times the number of groupers in a given space.

Mr Pay has come full circle. His business started in 1973 as a pig, chicken and food fish farm in Sembawang owned by his father. Mr Pay, who has Secondary 4 education, started helping out at the family farm when he was 10 years old.

He took over the business and started rearing koi in 1986 after a friend's farm shut down and he was given 20 breeder koi.

Mr Pay sold his first batch of groupers to wholesalers in 2013. He started rearing prawns last year. "Now, we are trying to breed lobsters and crabs. The plan is to open a live seafood market here soon," said the father of three.

Jessica Lim