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Brass Nets Spell an End to Algal Growth

AUSTRALIA - One Tasmanian salmon farmer has ceased using antimicrobials and anti-fouling paints with a revolutionary brass net to repel algal growth.

"We would be one of the only farms in the world to be antibiotic and anti-foulant free," Bruce Hogarth of Tasmania's northern-most salmon farm, Van Diemen Aquaculture, at Rowella on the Tamar Estuary, told ABC.

On ABC TV's 7.30 Report last night, reporter Connor Duffy exposed the quantities of antibiotics and anti-fouling paints used by some Tasmanian salmon farms, which undermine Tasmania's claims to being clean and green.

Owner and director of Van Diemen Aquaculture, Mr Hogarth says the use of anti-microbial chemicals has been huge concern to the industry globally and it is why his Tamar farm is differentiating itself on environmental lines.

Mr Hogarth says current-flows in the Tamar are significantly above those in other farmed areas of Tasmania, and that has proven to be an advantage.

"We've got a 3.5-metre tide range here and the ensuing water flow, water volume and water exchange is massive, and that's the thing that salmon like."

The average water flow at Rowella is 30 to 50 cm per second, and it does get up to 80 cm per second at peak runs of the tide. That has necessitated the use of more robust cages to hold the fish.

Mr Hogarth explained: "We're the only company in the world that use 100 per cent brass nets. With the brass nets, because it's 65 per cent copper, it repels most algae growth and lets in the full 100 per cent flow of the water. Because they weigh about 10 tonnes the nets retain their shape and they're also 100 per cent seal-proof.

"Because we don't have to anti-foul our nets, we do not use anti-foulants here on the farm and because of our pristine water flow through these clean nets we don't use antibiotics."

The market is continuing to grow strongly at about 12 to 15 per cent each year and Bruce Hogarth says their system has been so successful Van Diemen Aquaculture is now planning to trial a new site on the Tamar River.

A two-year trial growing young fish in brass cages anchored adjacent to Gunns planned pulp mill not far from the Batman Bridge is set to begin in August next year and continue until January 2012.

Mr Hogarth says it is the only other site in the Tamar that could be suitable for salmon.

General Manager of Water and Marine Resources in DPIPWE, Wes Ford, says Van Diemen Aquaculture has applied to amend the Tamar Estuary Marine Farming Development Plan to include a new marine farming zone that encompasses the permit site.

Mr Ford told ABC: "The permit will allow four fish cages to be placed on the eastern side of the Long Reach section of Tamar River. It will allow for a single year class of fish to be grown.

"Research in response to the amendment application indicated that more information is required before a determination could be made.

"High current flows are considered to be a positive factor in selection of fish farming sites, but some questions need to be considered in relation to the culture of young fish in these high velocities.

"The trial will allow these questions to be answered before an amendment is progressed under the provisions of the Marine Farming Planning Act 1995."

the Fish Site Editor

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