Marine Subsidies in Freshwater: Effects of Salmon Carcasses on Lipid Class and Fatty Acid Composition of Juvenile Coho Salmon

Abstract

Returning adult salmon represent an important source of energy, nutrients, and biochemicals to their natal streams and may therefore have a quantitative effect on the energy levels of stream-resident salmonids. We tested this hypothesis by constructing simulated streams for coho salmon Oncorhynchus kisutch to which we added 0, 1, and 4 carcasses/m² (0, 0.71, and 2.85 kg wet mass/m²) of pink salmon O. gorbuscha. After 60 d we evaluated the lipid class and fatty acid composition of rearing coho salmon from the simulated streams; the lipid content and triacylglycerols of the coho salmon increased with increasing carcass density whereas phospholipids decreased. Increased amounts of triacylglycerols accounted for most of the lipid increase. In addition to increasing in concentration, the fatty acid composition of the triacylglycerols also changed with carcass density. Triacylglycerols of juvenile coho salmon from the control streams had significantly higher omega-3 : omega-6 ratios as a result of fivefold and sixfold increases in the concentrations of eicosapentanoic and docosahexanoic fatty acids, respectively. These data demonstrate an immediate nutritional benefit resulting from the introduction of salmon carcasses in juvenile coho salmon rearing habitat and indicate the utility of fatty acid and lipid class analysis for examining the effects of marine-derived nutrients on juvenile salmonids.

Notes

² Fatty acids are often categorized by the number and locations of their double bonds. Fatty acids with the first double bond located three bonds from the methyl end of the chain are designated as omega-3 fatty acids; likewise, omega-6 fatty acids have a the first double bond located six bonds from the methyl end. In this report, fatty acids are identified as xx:a(n-b), where xx refers to the number of carbons in the chain, a to the number of double bonds, and b to the location of the first double bond from the methyl end