| Summary: | This study was undertaken to assess the use of carbon and nitrogen stable isotope analyses as methods to identify source host fish populations of sea lice, Lepeophtheirus salmonis. The delta carbon signatures of parasitic copepodid sea lice used to infect cultured Atlantic salmon in the laboratory were found to be statistically indistinguishable from the delta carbon signatures of blood (ANOVA, p = 1.000) and mucus (ANOVA, p = 0.430) sampled from the wild pink salmon population from which the sea lice originated. As a result, delta carbon signatures show potential as tools to track the movement of sea lice between fish populations. In contrast, delta nitrogen analysis did not show such promise as the natal host fish, wild pink salmon, and novel host fish, cultured Atlantic salmon, between which sea lice were transferred during the study, did not display distinct isotope signatures and thus could not be differentiated. This study found that when applying stable isotope analysis as a method to studying the dispersal of sea lice (1) the blood and mucus of potential source host fish populations should be sampled when assessing their possible relationship to sampled sea lice, (2) sea lice in no later than the parasitic copepodid stage should be analysed, (3) sea lice should be given time to clear their guts of any host materials before analysis takes place, (4) sea lice sampled from the gills should not be not grouped with sea lice sampled from the body surface or fins, and (5) replication unit for sampled parasitic copepodids should be set at the individual and not host fish level. The application of stable carbon isotopes to tracking the movement of sea lice between host fish is a promising method for directly identifying sources of sea lice epizootics and of quantifying the exchange of sea lice between host fish populations. Land and Food Systems, Faculty of Graduate
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