In fact, the fastest growing farmed salmon only reach harvestable size a few months earlier than the fastest growing wild salmon. Research made by Nutreco Aquaculture investigated the occurrence of cataracts and other abnormalities. The incident that raised cataracts as an issue was in 1995, when a number of fish in Ireland and Scotlandwere found to have them. Nutreco Aquaculture research showed that they were caused by wide fluctuations in the water temperature, which led to a doubling of the dietary requirement for a specific amino acid, histidine. 1995 was an unusually hot summer and no one had been aware of this effect before. We should mention that cataracts do occur in the wild salmon population as well. Diet adjustments have been made, increasing the levels of histidine, and cataract occurrence has not been a problem since that time.

On the question of abnormalities caused by the rate of growth, no evidence exists for this hypothesis. While abnormalities are sometimes found in farmed fish, these also occur in wild populations. However, a key difference is that the fish farmers monitor their fish and remove any with abnormalities, so we are more aware of them. We are investigating the causes of any abnormalities and these seem to be multi-factorial, that is the result of several factors such as combinations of environment and husbandry plus other possible influences. They are unusual, which makes tracing the causal factors more difficult. It is a very interesting issue but is not a direct result of improper farming practices.