the properties of fish faeces influenced by the quality of feed can be a risk for water purification in ras systems hjeltnes et al threats have to be taken seriously in worst case changes in the ecosystem food chains can be irreversible risks connected to genetic manipulations of either feed organisms or fed animals are a common concern for many consumers and scientists fears of human health risks with byproducts of animal husbandry cannot be brushed aside last but not least of the ethical worries is the net effect of aquaculture on the global protein supply