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Fish farms that stack up nicely

Researchers and students have come up with a stackable fish farm that is among the first such in the world. The method uses 1 sq m, connected cubes filled with water to rear fish on land, which saves space and allows farmers to control the water quality.

The cubes can be stacked up to four levels; the experimental farm in Choa Chu Kang, about the size of a football field, now produces up to eight tonnes of fish a year, but this can be ramped up to 36 tonnes.

Fish farmer Lee Van Voon, 45, who is partnering Singapore Polytechnic in the project, said his sea farm off Pulau Ubin is half the size but produces only one tonne of fish each year. Fish farmers said farms range in productivity but this is ‘on the low side’.

Since the land farm started operations in October, it has also slashed fish death rates from the usual 60 per cent in sea farms to less than 30 per cent.

Fish sellers said there is no difference in taste between the land-reared and sea-caught fish.

Other countries, notably Sri Lanka and Canada, have experimented with land-based fish farms, but these are typically large, sprawling farms.

Land farms in Singapore are likely to have a higher cost as farmers will have to pay monthly rent on land leased from the Government, whereas sea farms are subjected to only an annual licence fee.

Mr Lee, for example, is paying $3,000 a month for a plot of land the size of three football fields in Choa Chu Kang. A sea farm the same size would cost just slightly more than $2,500 a year. The infrastructure for both types of farms costs about the same.

But Mr Lee said the land farm would be more profitable in the long run because of the much higher production rate, and this can be increased with stronger cubes that can be stacked higher.

The new method also allows farmers to beat nature’s whims. ‘During storms, rainwater can wash mud into the sea farms. Plankton can also suddenly bloom and poison the fish,’ he said.

Farmers told The Sunday Times it is common for half of their fish to die within a week of purchase. Ms Maureen Ng, in her 60s, who owns a fish farm off Punggol, said: ‘If we have 50 per cent still alive by the time they are ready to be sold, we are happy.’

The new system uses bio-materials such as stones, algae and sunlight to regulate nutrients in the water. The tanks are linked through water pipes, but individual tanks can be isolated in case of bacteria outbreaks.

Project leader Desmond Lim, 50, a senior research engineer at the Singapore Polytechnic’s Centre for Applications in Environmental Technology, said no chemicals are used and the water can be recycled for up to six months. Waste from the fish is consumed by enzymes in the water. ‘After each batch of fish, we also change the water for food security, in case there were viruses in the old batch,’ he said.

But there are limitations. The cubes’ 1m dimensions mean they cannot be used to rear larger fish such as the popular edible cobia.

Making the tanks larger would result in water pressure that may cause danger to the walls, Mr Lee said.

The system also cannot support cold-water fish such as salmon and trout because chilling the water to the required temperature would be too expensive.

The farm rears tilapia and marbled goby fishes, popular edible species in Singapore. It sold its first batch of fish earlier this month.

Mr Timothy Ng, president of the Fish Farmers Association of Singapore, said the method could encourage more sea-based fish farmers to switch to land farms, provided they rear suitable fish and it is more profitable.

The Singapore Polytechnic team was awarded $10,000 by the school to develop the idea.

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