To investigate the relationship between metabolic changes in $^1H$-nuclear magnetic resonance (NMR) spectra and fish vaccination, serum was collected from olive flounders treated with a formalin-killed Edwardsiella tarda vaccine and used for $^1H$-NMR metabolite profiling. Principal component analysis and partial least squares were applied to the $^1H$-NMR profile to reduce its complexity and establish class-related clusters. Relative lipid regions were distinguished in vaccinated and non-vaccinated serum. Then, the lipids were extracted from the serum and analyzed. Triolein was identified.