Fish used to grow veges

ALASTAIR PAULIN

BUMPER HARVEST: Aquaponics pioneer Dr Wilson Lennard, centre, with Tasman Bay Herbs owner Don Grant and technician Annalise Runarsson in the Riwaka trial greenhouse.

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An innovative trial in Riwaka is testing the benefits of growing vegetables from fish waste.

Tasman Bay Herbs is hosting the trial, which is the first in the world to successfully grow both plants and fish using a system designed by Australian scientist Dr Wilson Lennard.

The trial is comparing the success of traditional hydroponics, which is how Tasman Bay Herbs grows 90 per cent of its products, to Dr Lennard's aquaponic system.

The first crops of salad greens were harvested on Thursday and preliminary results showed that the aquaponic crop grew faster, better and with no "tip burn", a key sign of high quality, Tasman Bay Herbs owner Don Grant said.

At stake is not just the bet between the two men over whether aquaponics would be as productive as hydroponics but the potential for aquaponics to produce fish and fresh vegetables in a small area of land with highly efficient use of water.

"We see this as a template to be able to one day produce food in the middle of cities, especially countries where they have water and food shortages," said Mr Grant, who usually goes by the title of Tasman Bay Herbs' "chief ideas bloke".

With funding from the Berrysmith Foundation, which promotes sustainable agriculture, Tasman Bay Herbs set up a trial greenhouse and Dr Lennard implemented his system. Between them, the foundation and Tasman Bay Herbs had invested around $400,000 in the trial, said Mr Grant.

Four 1700-litre tanks hold grass carp, a tough fish that is the second-most eaten freshwater fish in the world, popular in Asia and Eastern Europe. Eighty per cent of the carp's waste is ammonia that is emitted through its gills and the ammonia-rich water is pumped through a series of filters, including a tank of polystyrene beanbag balls coated with a naturally occurring bacteria that converts the ammonia to nitrates.

The nitrate-rich water is then pumped through a standard hydroponic system which grows plants in a thin film of water. A key advantage of Dr Lennard's proprietary technology is that it "bolts-on" to the largest hydroponic growing system in the world, he said.

The plants take up the nitrates and filter the water, which is then returned to the fish tanks. Because of the system's closed loop, no sprays can be used on the plants, making it "beyond organics", Mr Grant said. It also means no water is lost, making the system safe to use in highly populated areas and miserly in water consumption.

Dr Lennard, who is one of three scientists in the world publishing on aquaponics, said what made his system unique was the design and management techniques that balanced the inputs – the number of fish, with the outputs – the amount of food grown.

"If you get a balanced system, it uses the least amount of water and it uses all the nutrients," said Dr Lennard.

Tasman Bay Herbs has had the system approved by an auditor from the New Zealand Food Safety Authority, making it the first time in the world a regulatory body had approved such a system, he said.

Tasman Bay Herbs plans to scale up the trial to grow herbs commercially, including dill, italian parsley and coriander. By the end of the year, the company's chief herb grower, Yoka De Houwer, will decide whether to convert the company's main greenhouse to the aquaponic system.

If that happens, Mr Grant said "all of a sudden, we'd have a small market for fresh fish". Although it is too early to say how much it would cost to convert from hydroponics to aquaponics, Mr Grant said he believed there would be a financial pay-off from better growth and more efficient resource use, as well as being able to sell the fish. He plans to work with chefs to see if the fish is suitable for restaurants, and is also looking at alternative species both as nutrient providers and food.

The Berrysmith Foundation is also researching a fish food pellet that could be made from plant waste produced by an aquaponic system, which would "close the sustainability gap", Mr Grant said.

- © Fairfax NZ News