Elemental analysis of Scottish populations of the ectoparasitic copepod Lepeophtheirus salmonis

Conventional nebulisation ICPMS (Inductively Coupled Plasma Mass Spectrometry), was used to determine the concentration of a broad range of elements in the salmon louse Lepeophtheirus salmonis. Lice samples were collected from Atlantic salmon in seven localities (4 fish farms and 3 wild salmon fisheries) on two separate sampling occasions and prepared for analysis. Sixty six elements were measured, 35 of these were found to be variable and were subjected to univariate and multivariate statistical analysis. The results of the single element comparisons showed that not all individual sites could be discriminated from each other. Sea lice collected from cultured salmonids could be discriminated from those on wild salmonids at the same site using the elements magnesium (<0.05%), vanadium (<0.01 %) and uranium (<0.05%). Using discriminant analysis based on 28 elements, the separation of all sampled sea lice localities from each other was clear (100% correct classification) giving each an individual signature. Further analysis examined the effects of sequentially removing elements from the discrimination model in order to determine the minimum number of elements required to obtain satisfactory discrimination of populations. It was found that 16 elements could still provide 100% correct classification, whilst 12 elements still provided 97.30% correct classification. This pilot study has shown elemental analysis to be a potentially successful method for the discrimination of populations of L. salmonis, although the biological basis of the elemental signatures derived remains to be established.