Geographic variation in trace elements in scales of pre-smolt farmed Atlantic salmon

The Norwegian aquaculture management authorities’ need a method that enables the identification of escaped farmed salmon caught in sea or in the river systems. A method based on the natural variation of incorporated trace... [ view full abstract ]

The Norwegian aquaculture management authorities’ need a method that enables the identification of escaped farmed salmon caught in sea or in the river systems. A method based on the natural variation of incorporated trace elements in the salmon scale is under development.
The growth pattern, of the mineralized layer on the fish scale, has radical increments (sclerites) quite analogue to tree rings. While a tree forms a new ring on a yearly basis, a new sclerite is formed every 7-8 days. The trace element content in these mineralized growth bands of the scale reflects those present in the ambient water at the time of creation.
The chemical variation of 12 elements in sclerites of salmon scales has been analysed by laser-ablation-ICPMS. Eighteen hatcheries distributed along the entire Norwegian coastline are included in the survey, making this the largest study ever published on fish-scale chemistry linked to geographic variation. Based on robust multivariate statistical analysis 97% of the smolt was correct identified to its hatchery. Of 1347 scale analyses only 44 were misplaced in relation to its origin. Strontium and barium are the most important elements for group separation. Floodplain sediments at the south-western coastline of Norway show elevated lead-values compared to the remaining coastline. In this area the majority of the scales show values of lead above detection limit. Scale chemistry may provide a tool to determine the origin of escaped Atlantic salmon, however further investigations are needed before this method can be implemented in the salmon management in Norway.