Abstract

Over the past decade the role parasites play in ecosystems has gained increased attention, but in terms of an isotopic approach to trophic ecology they still lag far behind their free-living counterparts. Swordfish offer the unique opportunity to study the trophic relationships within a host-parasite system because their parasites are relatively well known, they have varied feeding ecology, and there is a high incidence of multiple co-infections within the same organ (e.g., stomach). We opportunistically sampled the stomachs of 33 Swordfish landed at the Mississippi Gulf Coast Billfish Classic in 2017 and 2018. A total of nine species of parasite were found either in the stomach or attached exterior to the stomach; including 5 species of nematode (3 as adults), 2 species of larval cestode (one that occurred within the stomach and one associated with the body cavity), and one species each of a trematode and an acanthocephalan. The adult nematodes Hysterothylacium incurvum and H. corrugatum had the highest prevalence of infections at 81% (95%CI 63–92%) and 59% (95%CI 41–76%), respectively, the highest mean abundances (16.3 ± 3.4 and 11.4 ± 2.6, respectively), and highest mean intensity of infections (20.0 ± 3.8 and 19.2 ± 3.5, respectively) of all other parasite taxa. The congeners co-occurred in 56% of samples, but there were no differences in any of the parasite metrics based on host sex. We hypothesize that the trophic position of these co-occurring parasites will vary based on their different feeding strategies (feeding on host prey items, absorptive feeding on macronutrients, or feeding directly on the host) and their development stage (larval vs adult). This approach should provide additional insight into how two congeners can occupy the same habitat in a host and if any resource partitioning occurs

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