Consumption of marine-derived nutrients from invasive Chinook salmon (Oncorhynchus tshawytscha) transfer ω-3 highly unsaturated fatty acids to invasive resident rainbow trout (O. mykiss)

Abstract

Marine-derived nutrients (MDN) contained in gametes (mature eggs and sperm), carcasses and metabolic wastes from anadromous migratory salmon can transfer energy and materials to fresh water, thereby affecting the structure and function of stream ecosystems. This is crucial among ecosystems where humans have mediated biological invasions by propagating non-native species. Previous studies have demonstrated that consumption of MDN from salmon can benefit both native and invasive resident fishes. Yet, a more detailed understanding of the transfer of biomolecules with important physiological functions such as ω-3 highly unsaturated fatty acids (HUFAs) have received less attention among researchers. Here we demonstrate that consumption of MDN contained in invasive Chinook salmon eggs transfers ω-3 HUFAs (e.g., EPA and DHA) to resident invasive rainbow trout in a river food web. We conducted a field study in river sections previously identified as spawning areas for Chinook salmon in the Cisnes River, Patagonia. Rainbow trout were sampled around salmon spawning areas before, during, and after the salmon spawning season. Additionally, we collected tissue from different food web resources and components of different origin (e.g., primary producers, aquatic and terrestrial items) from the Cisnes River system. Analyses of stomach contents of trout were performed in conjunction with analyses of both lipid content and fatty acid profiles of trout tissue and food web components. Chinook salmon eggs showed higher content of ω-3 HUFAs, especially EPA (31.08 ± 23.08 mg g DW^-1) and DHA (27.50 ± 14.11 mg g DW^-1) than either freshwater or terrestrial components (0-6.10 mg g DW^-1 both EPA and DHA). We detected marked shifts in the fatty acid profile (~six-fold increase in EPA and DHA) of trout following consumption of Chinook salmon eggs. Our findings suggest that MDN via consumption of salmon eggs by resident rainbow trout may positively influence resident trout and likely contribute to gauge synergistic interactions between invaders on receiving ecosystems of Patagonia.

Keywords: Anadromous; Ecophysiology; Food webs; Non-native species; Ocean; Salmonids.