Farming fish and greens together

This water-circle system grows vegetables hydroponically, using nutrients in farmed fish waste

By Natalie Soh

FARM both fish and vegetables on a small plot of land and get yields four times better than ordinary farms.

It sounds almost too good to be true, but that is exactly what Mr Tan Say Meng has done with the help of some science and technology.

'We are trying to combine two types of cultivation - fish and vegetables - scientifically,' said the 33-year-old.

He has set up a 'water-circle system' on his 1,500 sq m pilot-project farm in Sembawang.

In what is believed to be the first of its kind in Singapore, his farm uses certain waste products from farmed fish to grow vegetables hydroponically.

With special pumps, he is able to increase the oxygen content in the fish tanks. So, in one tonne of water, he can pack and rear 30 freshwater fish, such as tilapia. Traditional fish farms support 10 fish per tonne of water.

'It's a farmer's secret: We don't use the solid waste from the fish - we filter all of that out,' he said.

It is the ammonia in the water that is valuable. Using a special bacteria, the ammonia is first broken down to nitrite nitrogen then, in turn, to simpler nitrates.

This nitrate-rich water is then pumped to a hydroponic system, where the vegetables thrive on the nutrients.

He is growing exotic varieties of lettuce, such as buttercrunch, red oak and green coral as well as tomatoes, carrots and herbs.

The plants absorb the nitrates, effectively cleaning the water. The water is then pumped back into the fish tanks.

'This way, we conserve water because the only loss is through evaporation,' he said.

The 9 sq m space devoted to growing the organic vegetables produces 100 to 150 kg of each type of produce per month.

For the same space, traditional soil farming only produces 25 kg of produce, said Ms Poh Bee Ling, senior research officer with the Agri-food and Veterinary Authority of Singapore (AVA).

Mr Tan's main customers are restaurants and caterers. He pumps back 30 per cent of his returns into research and development.

He said: 'The system has to be worked out and refined - like an art form. You cannot rest on your laurels even when the system is working well, you have to continually innovate and learn new techniques to keep at the forefront of the field.'

He has also tendered for some land because he wants to expand into a full-scale commercial plant.

'That way, we can really see the work bearing fruit.'