Thursday, 25 October 2012

Sustainable aquaponics shifts to silver perch

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aqua ponicsThe water, being ready-fertilised, is then used to irrigate lettuces grown in NFT (Nutrient Film Technique) channels. Image: Erin MaloneCHALLENGER Institute of Technology is continuing an experimental aquaponics program, based at its Murdoch Campus.

Program coordinator Tony Bart says last year the institute produced 470 kilograms of restaurant-quality barramundi (Lates calcarifer) and 1320 hydroponic lettuces (Lactuca sativa).

As the barramundi is a warm-water fish, the project employed the greenhouse principle to heat the water, extra insulation to mitigate heat loss, and electric boosters to maintain water temperature during Perth’s colder months.

Mr Bart says the project’s focus has shifted this year to silver perch (Bidyanus bidyanus), a temperate-climate fish that does not require artificial water heating in winter.

Mr Bart says the institute has also installed 20 photovoltaic panels which produce five kilowatts of electricity.

“[It’s] powering the pumps and the blower during the daylight hours,” he says.

The fish begin as broodstock held in tanks at Toodyay.

“We inject them with a hormone called HCG (human chorionic gonadotropin),” he says.

They then generally take two days to spawn, before the larva are taken to the intitute’s hatchery in Fremantle.

“Once they hatch out we’ve got to take them through the larval process which is very intensive,” Mr Bart says.

“We’ve actually got to grow the live feed (brine shrimp, Artemia spp) to feed the fish.”

“It takes about 30 days, that’s very intensive but we’ve got to grow the Artemia and then we’ve got to actually enrich the Artemia to ensure a high survival rate [of silver perch],” he says.

“Their [Artemia’s] movement attracts the larvae and then they hit it—they eat it.

“Later on we wean them off live feed on to artificial feed.

“What’s innovative in this sense is that we are doing all the culture now in tanks, whereas in the farms they get the larvae to a certain size then they release them into ponds.

“Those ponds have natural phytoplankton and zooplankton blooms and they just fend for themselves, but by doing it all in tanks here obviously we have control of predators et cetera.

When the larvae grow to fingerlings they are transferred to the tanks at the Murdoch campus and weaned on to dry pellet feed.

He said the water from the tanks is recirculated through a biofilter system which converts the harmful ammonia and nitrite produced by the fish into nitrates which the plants use as food.

The water, being ready-fertilised, is then used to irrigate lettuces grown in NFT (Nutrient Film Technique) channels.

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