Individual energetic limitations in variable environments lead to life-history trade-offs between investment in somatic growth and gonadal tissue, causing individuals to adopt specific behavioural tactics to attain reproduction. We investigated energy allocation in primary and secondary sexual traits in Atlantic salmon by estimating the life history characters (smolt size, sea age, first sea year growth rate) by back-calculation of scales. Adult size increased with the fish sea age (years at sea) and exerted a strong allometric effect on the energy investment pattern into secondary sexual traits. A compensatory mechanism at the ejaculate level is identified by which males investing less in secondary sexual traits produce ejaculates of higher quality. Distinct differences in investment into primary and secondary sexual traits between the fish that spent a single year in the sea before returning to the spawn (grilse) and multi-sea-year adults were detected, indicating that their energy allocation strategy in reproductive effort reflects alternative developmental pathways. Grilse ejaculate investment depended more on the resource allocation, whereas multi-sea-year male ejaculate investment depended more on the resource acquisition.