Elemental analysis of Scottish populations of the ectoparasitic copepod Lepeophtheirus salmonis

Conventional nebulisation ICPMS (Inductively Coupled Plasma Mass Spectromet ry), was used to determine the concentration of a broad range of elements i n the salmon louse Lepeophtheirus salmonis. Lice samples were collected fro m Atlantic salmon in seven localities (4 fish farms and 3 wild salmon fishe ries) on two separate sampling occasions and prepared for analysis. Sixty s ix elements were measured, 35 of these were found to be variable and were s ubjected to univariate and multivariate statistical analysis. The results o f the single element comparisons showed that not all individual sites could be discriminated from each other. Sea lice collected from cultured salmoni ds could be discriminated from those on wild salmonids at the same site usi ng the elements magnesium (<0.05%), vanadium (<0.01%) and uranium (<0.05%). Using discriminant analysis based on 28 elements, the separation of all sa mpled sea lice localities from each other was clear (100% correct classific ation) giving each an individual signature. Further analysis examined the e ffects of sequentially removing elements from the discrimination model in o rder to determine the minimum number of elements required to obtain satisfa ctory discrimination of populations. It was found that 16 elements could st ill provide 100% correct classification, whilst 12 elements still provided 97.30% correct classification. This pilot study has shown elemental analysi s to be a potentially successful method for the discrimination of populatio ns of L. salmonis, although the biological basis of the elemental signature s derived remains to be established.