Change of climate is expected to influence the energy content of fish by affecting the environmental conditions  here lipids are produced, transferred, accumulated and consumed. We examined the lipid content of the Baltic herring (Clupea harengus membras) spawning in the Archipelago Sea during a period of declining salinity, high variability in temperature, and increasing population size in the Bothnian Sea. Contemporary samplings of zooplankton in the feeding area (Mäkinen et al. 2017) enabled comparisons of fatty acid (FA) composition between herring and its prey Limnocalanus macrurus, which forms a major source of energy in the Bothnian Sea in May-June (Rajasilta et al. 2015).