Having done some more searches on the subject of fish farming there is contoversy about the "conversion" rate.
Here is another link to an article on conversion which contains three figues and one from the industry to balance things.
RB
http://www.davidsuzuki.org/Oceans/Fi...n/Net_Loss.asp
Net loss of wild fish to produce farmed salmon
A total of 2.7 to 3.5 tonnes of wild fish are used to make 1 tonne of farmed salmon
ABSTRACT
"Since a salmon farm in BC currently uses between 1.3 and 1.7 tonnes of dry feed (ie: FCR of 1.3 to 1.7) to make one tonne of farmed salmon, then the total amount of wild fish used to make one tonne salmon is between 2.7 and 3.5 tonnes (ie: the FCR multiplied by 2.08). It should be noted that in practice, BC salmon farms do not often reach the lower FCR of 1.3 which is achievable only when feed is used very efficiently on the farm. Rather than taking pressure off ocean resources then, salmon farming is currently adding greatly to that pressure..........................Much more research needs to be done and it is unclear when, or if the day will come when farmed salmon will be vegetarian. In the meantime, the stress on the ocean ecosystem will increase as salmon aquaculture expands globally. The consumption of 6.2 tonnes of wild fish for each tonne of salmon produced not only means less food for humans, but also for the many ocean species that rely on these fish as part of their food chain. Currently, the continued expansion of salmon farming is not sustainable.."
http://www.wfga.net/issues.asp?id=37
The Environmental Impact Of Salmon Farms