ABSTRACT: Energetic tradeoffs between life-history traits, mediated by body reserves, vary across an inividual’s life. We quantified 2 fat stores in 3 life stages of Atlantic herring Clupea harengus to understand their importance for fuelling growth and reproduction. We determined how the magnitude of both stores changed with body size in immature, maturing virgin, and mature herring using 2 complementary sources of data: (1) validated industry data on muscle fat content in ‘maatjes’ (assumed here to represent maturing virgins) and mature her ring from 2013 to 2021; and (2) scientific data on mesenteric fat index in immature, maturing virgin, and mature herring from 2004 to 2019. Maturing virgin herring had 3% higher muscle fat reserves than mature herring and larger mesenteric fat reserves than either immature or mature herring, illustrating the importance of both fat stores at the onset of sexual maturation. Smaller mature herring had more mesenteric fat than larger mature herring, suggesting that this store is important for fuelling somatic growth. The dual-fuel strategy adopted by maturing virgin herring allows the energetic demands associated with puberty and somatic growth to be met simultaneously. This distinctive allocation strategy contributes to the unique flavour and commercial value of the ‘maatjes’ herring delicacy.