Enteroparasitic fauna of non-native Chinook salmon (Oncorhynchus tshawytscha) on the Chilean coast: host-parasite networks and the potential for spillback

Invasive species can disrupt disease dynamics in new areas. Upon introduction, an invasive species in its new range may be colonised by novel parasites that normally infect native fauna. If the infected invasive host then helps to spread and boost the parasites to native hosts, this is known as spillback. Chinook salmon ( Oncorhynchus tshawytscha ) were released into rivers in southern Chile around 1924 and became invasive from 39°S to 53°S. Its anadromous migration and predatory behaviour involve multiple interactions with various native species. We examined the digestive tracts from 114 adult Chinook salmon returning from the sea to the estuary in the Toltén River, Chile to characterise their enteroparasite diversity, classify parasite developmental stages and assess Chinook’s potential as a definitive host for local, native parasites. We enumerated 12,277 larvae of parasitic individuals belonging to the genera Anisakis and Hysterothylacium (Nematoda), Nybelinia (Cestoda) and orders Pseudophyllidea, Tetraphyllidea and Trypanorhyncha (Cestoda). Amongst these, we also found adults — one immature female, four gravid females and eight males of the nematode Hysterothylacium sp., six adults of the trematodes Lecithaster sp. and one Lampritrema sp. Finding advanced and adult stages suggests chinook are a competent non-native host for Hysterothylacium , Lecithaster and Lampritrema , as well as a non-native host for larval stages of Nybelinia sp., Pseudophyllidea and Tetraphyllidea. Our study demonstrates the integration of native parasites into an invasive host along the coast of Chile. Namely, Chinook salmon are now acting as a novel host that is positioned as a new node in trophic interactions and host-parasite networks. Additionally, our study provides valuable baseline data for further research on the impact of these parasites on native species and ecosystem dynamics, including the extent to which spillback is occurring.