Mr. Donal Maguire:

In addition, a very difficult technology is used in recirculation to strip out the nutrients in the water and it does not work properly with salt water because one must use bacteria in a living system. It is a bit like using a giant septic tank system, if members will pardon the indelicacy, to clean the water. As for making such a system work in sea water, they are getting big crashes whereby the system works for a while and then stops working all of a sudden. One then gets toxicity in the water and the fish die. The other thing is that to make these recirculations systems work, the fish are stocked at extremely high densities. In a salmon cage in the sea in an Irish organic salmon farm, there are 10 kg of salmon to a cubic metre of water, so that is 1% salmon and 99% water. They must stock them at ten or 20 times this density to make these tank systems pay. Therefore, if the system does not work perfectly, one gets a giant fish mortality really fast. Therefore, it is quite high-risk stuff and highly technologically based and if there is any slight fault, there can be huge consequences for the farm.