Iron and manganese toxicity in salmonids - problem overview and possible solutions for the aquaculture industry

Iron toxicity is a serious and incrasing problem for smolt-production in Norway. Precipitation of iron on fish-gills, gill-damage and fish kills has been documented. Problems with massive mortality are mostly related to hatching and the juvenile stages. H owever, in older fish more diffuse gill-problems are often reported. Iron toxicity is mostly related to the presence of ferrous iron (Fe II), and the oxidation of ferrous to ferric (Fe (III) iron. Furthermore, the presence of Fe (II) can cause tissue dama ge through free radical formation and lipid peroxidation. Temperature and pH are important modifiers of iron toxicity, and during winter and snowmelt the combined effects of low temperature and low pH can cause relatively high concentrations of toxic Fe ( II). Like iron, manganesechemistry is also characterised by redox transformations, and has been shown to have negative effects on fish. In this project we will work experimentally to gain a better understanding of the causes and mechanisms of iron and manganese toxicity. Different methods to reduce toxicity will also be tested and compared. Pilot-studies have shown significantly reduced Fe-accumulation on fish gills by trating iron-rich water with basic silicate (Water-glass"). T his method will be further evaluated and tested.