Containment – From the Archive
A STORY FROM 1979 ABOUT TRIAL- LING COPPER NICKEL CAGES AT ARDTOE
F
ISH farming researchers on the West Coast of Scotland have started a trial to assess the value of copper nickel
sea cages for growing fl atfi sh and shellfi sh.
One centre taking part in the trial is the White Fish Authority Marine Farming Unit at Ardtoe, Acharacle, Argyll. The experiments are at an early stage.
The cage being used is 1.8 metres square and is 1.2 metres deep. The mesh is 16 gauge copper nickel wire with a 12.7mm square mesh size. The fl oor area is of glass fi bre with a copper nickel mesh panel set in the centre.
‘Our trial has just been set up and the cage has been immersed for only a few weeks. ‘We put fi sh into it at the end of August after the recommended “leaching out” period had been completed’, said Mr Steven Hull, offi cer in charge at Ardtoe. ‘I have an open mind on this mate-
rial. There is of course the toxicity factor which needs assessment. This would be more critical in shellfi sh farming than in fi nfi sh. ‘However it will be interesting to see the effects of direct contact by the turbot on the copper nickel mesh area on the cage fl oor. ‘If all this proves not to be a prob- lem then the anti-fouling properties of copper nickel, its long in-sea life and the reduced maintenance requirement might well outweigh the initial high capital cost of the cage for the fi sh farmer. However it
is at the moment a question of wait and see,’ he said.
The International Copper Re-
search Association (INCRA) have been carrying out experiments with similar cages for some time. A prototype model has now successfully weathered two fi erce winters in a fi sh farm off the coast of Maine, USA and fi ve more copper nickel cages are being built for testing at fi sh farming sites in Scotland.
BIOFOULING
‘The Maine cage was created to combat a number of the major problems of aquaculturists, including the most serious technical one, that of biofouling. Most fl oating fi sh enclosures are made of nylon net. ‘This biofouls easily. It fi lls up with algae and other aquatic plant life and acts as a setting material for various marine creatures, particu- larly mussels’, says INCRA. ‘This can greatly decrease the
supply of oxygen and water-borne nutrients to the fi sh cash crop while increasing the weight of the net, possibly leading to its breaking.’ The INCRA cage at Maine was put in the water on July 22, 1977
www.fishfarmer-magazine.com
and let sit for two weeks without fi sh to reduce to a minimum any detrimen- tal effects of copper. During this time it was noted that all fouling disappeared from the nearby conventional net cages, but the fi sh in them were not adverse- ly affected.
After the initial two
weeks the cage was stocked with salmon. It was to be comparative tested against conven- tional nylon bag pens used to hold the fi sh during their grow-out phase.
This test ran
through the spring of 1978. During this time the salmon in the copper nickel cage had growth rates, health and vigour at least as good, if not better, than those in the conven- tional pens at comparable stocking densities, according to INCRA. The cage is currently stocked with fi sh at a medium to high density and they continue to do well. The cage proved to hold up
much better even than it was expected to. During the winter of 1978 the system survived six major storms which long-time Maine residents said were the worst in at least 100 years. It withstood conditions far beyond its design requirements with only minor damage to the walkway fi xtures. FF
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