The Ross Sea, Eastern Antarctica, is considered a “pristine ecosystem” and a biodiversity “hotspot”
scarcely impacted by humans. The sibling species Contracaecum osculatum sp. D and C. osculatum sp. E
are anisakid parasites embedded in the natural Antarctic marine ecosystem. Aims of this study were to:
identify the larvae of C. osculatum (s.l.) recovered in fish hosts during the XXVII Italian Expedition to
Antarctica (2011e2012); perform a comparative analysis of the contemporary parasitic load and genetic
variability estimates of C. osculatum sp. D and C. osculatum sp. E with respect to samples collected during
the expedition of 1993e1994; to provide ecological data on these parasites. 200 fish specimens (Chionodraco
hamatus, Trematomus bernacchii, Trematomus hansoni, Trematomus newnesi) were analysed for
Contracaecum sp. larvae, identified at species level by allozyme diagnostic markers and sequences
analysis of the mtDNA cox2 gene.
Statistically significant differences were found between the occurrence of C. osculatum sp. D and
C. osculatum sp. E in different fish species. C. osculatum sp. E was more prevalent in T. bernacchii; while, a
higher percentage of C. osculatum sp. D occurred in Ch. hamatus and T. hansoni. The two species also
showed differences in the host infection site: C. osculatum sp. D showed higher percentage of infection in
the fish liver. High genetic variability values at both nuclear and mitochondrial level were found in the
two species in both sampling periods. The parasitic infection levels by C. osculatum sp. D and sp. E and
their estimates of genetic variability showed no statistically significant variation over a temporal scale
(2012 versus 1994). This suggests that the low habitat disturbance of the Antarctic region permits the
maintenance of stable ecosystem trophic webs, which contributes to the maintenance of a large populations
of anisakid nematodes with high genetic variability.