Across existing fish host-parasite literature, endoparasites were depleted in δ15 N compared to their hosts, while ectoparasitic values demonstrated enrichment, depletion and equivalence relative to their hosts. δ13 C enrichment varied extensively for both endo- and ectoparasites across taxa and host tissues. In our case study, sea lice (Lepeophtheirus salmonis) were enriched in δ15 N relative to their farmed Atlantic salmon (Salmo salar) hosts, although the value contradicted the average that is currently assumed across the animal kingdom. Common fish lice (Argulus foliaceus) did not show a consistent trend in δ15 N compared to their wild S. salar hosts. Both parasitic species had a range of δ13 C enrichment patterns relative to their hosts. Farmed and wild S. salar had contrasting δ13 C and δ15 N, and signals varied across muscle, fin and skin within both groups. L. salmonis and A. foliaceus subsequently had unique δ13 C and δ15 N, and L. salmonis from opposite US coasts differed in δ15 N. Given the range of enrichment patterns that were exhibited across the literature and in our study system, trophic dynamics from host to parasite do not conform to traditional prey to predator standards. Furthermore, there does not appear to be a universal enrichment pathway for δ13 C nor δ15 N in parasitic relationships, which emphasizes the need to investigate host-parasite linkages across species.
Keywords: louse; parasite; salmonid; trophic enrichment; δ13C; δ15N.
© 2020 Fisheries Society of the British Isles.