Published by City Farmer, Canada's Office of Urban Agriculture
Roofwater Fish Farm Ideal For Learning
An Agrovision Publishing Report
Geoff Wilson,
Executive Officer (honorary),
The Urban Agriculture Network - Western Pacific Office,
PO Box 85,
Mt Gravatt Central,
Queensland 4122,
Australia.
Phone 61 7 3349 1422
Fax: 61 3343 8287
Mobile: 0412 622 779
fawmpl@powerup.com.au
Scientist Vivienne Hallman on periurban acres at Figtree Pocket, 10 kilometres from the Brisbane CBD, is proving that urban fringe farmers can grow native fish successfully on natural foods.
Most of the water can come from a home rooftop. Much of the fish food can be home-grown earthworms and insect larvae.
Vivienne's project has shown how Australian native fish could be reared in a small area on worm-farmed kitchen scraps - to give benefits to a vegetable or fruit tree garden.
But her story is also instructive from the point of view of starting up a fish farm in a backyard or an urban fringe (periurban) farm - or even on a larger farm, where diversification is possible.
I believe the fish farm of 25,000 litres of tank space is the ideal next learning step for an intending fish farmer who has learned enough from an indoor fish tank and wishes to become more serious.
It is probably the best way to ease into a larger fish farm investment, while reading avidly and even studying aquaculture by correspondence.
Vivienne started her fish production unit in 1991 as part of a fish farming research project associated with Kevin Warburton of the University of Queensland.
The project was to see how dairy farm wastes could be used to grow natural fish foods - so that purchasing of expensive, bought-in fish foods could be avoided.
Features of her fringe farm unit now are:
- It has harvesting of rooftop water from her home - into an above-ground pool that holds at least 50,000 litres. About 25mm of rain yields 10,000 or so litres at a time. Minimal town water supplement is needed (and could perhaps be replaced by further water harvesting.
- It has five above-ground tanks (former above-ground pools) each holding about 4,000 litres and up to 50 fish.
- Silver perch, a native warm-water species, is grown from fingerlings to a plate size of 350 to 400 grams.
- Fish are fed earthworms, insect larvae and pelleted food. They also have natural food from pond life which develops in the five tanks.
- As water is fouled by fish excreta and decomposing food waste, it is used to irrigate vegetables and fruit trees, which also gain from additional fertiliser from worm castings.
- Water flow is mostly by gravity, the exception being the pumping of orchard irrigation water using a small petrol-motor powering a pump.
How many fish meals can Vivienne's small fish farm produce in a year ?
The answer depends on how much feed can be produced and the water temperature.
"One crop a year of silver perch is possible with unheated water," she said. Up to 50 fish a year can be raised in a 4,000-litre, unheated tank, to 350 to 400 gram size.
"This means each of my five tanks is capable of raising 17 to 20 kg of silver perch under the non-stressful growing conditions I favour," Vivienne said.
"It's a total potential output of 80 to 100 kgs - more than enough for my family's needs, plus the potential of a small saleable surplus."
That potential surplus could also be improved if simple solar heaters could warm the water during Brisbane's mild winters. Two crops of fish a year might then be possible, providing the food supply was improved also.
However, Vivienne has never produced a surplus because her work has focused on harvesting scientific information rather than fish.
Her main interest, after all, is being a consultant with a rare depth of understanding of both scientific and the practical systems.
Besides earning a masters degree of engineering science in environmental engineering from Griffith University in 1997, she obtained a bachelor of science degree from Sydney University in 1964.
Balancing these are her Permaculture consultant qualifications and worm farming experience.
Vivienne set up and managed the innovative worm farm at International House, at the University of Queensland, where the food scraps from meals for around 100 students were converted into nutrients for a Permaculture garden.
This urban farming opportunity will be the subject of a story in the next issue - in both small and large-scale applications to food waste management.
But Vivienne is also well-focused on mainstream agriculture. Her environmental engineering degree thesis, was on the suitability of earthworms for recycling solid and liquid waste from the dairy industry.
That too, could involve fish farming - and the type of small scale learning experience that is relatively easy to set up on an existing dairy farm with reasonable rainfall.
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