Following general life history theory, immediate reproductive investment (egg mass Ã fecundity/body mass) in oviparous tele- osts is a consequence of both present and past environmental influences. This clarification questions the frequent use of sea- son-independent (general) fecundity formulas in marine fish re- cruitment studies based on body metrics only. Here we test the underlying assumption of no lag effect on gametogenesis in the planktivorous, determinate-fecundity Atlantic herring (Clupea harengus) displaying large plasticity in egg mass and fecundity, examining Norwegian summer-autumn spawning herring (NASH), North Sea autumn-spawning herring (NSAH), and Norwegian spring-spawning herring (NSSH). No prior reproductive informa- tion existed for NASH. Compared with the 1960s, recent reproduc- tive investment had dropped markedly, especially for NSAH, likely reflecting long-term changes in zooplankton biography and pro- ductivity. As egg mass was characteristically small for autumn spawners, although large for spring spawners (cf. different larval feeding conditions), fecundity was the most dynamic factor within reproductive investment. For the data-rich NSSH, we showed evi- dence that transient, major declines in zooplankton abundance resulted in low fecundity over several subsequent seasons, even if Fulton's condition factor (K) turned high. Temporal trends in Kslope (K on total length) were, however, informative. These re- sults clarify that fecundity is defined by (i) dynamics of primary (standing stock) oocytes and (ii) down-regulation of secondary oo- cytes, both processes intimately linked to environmental conditions but operating at different timescales. Thus, general fecundity for- mulas typically understate interannual variability in actual fecun- dity. We therefore argue for the use of segmented fecundity formulas linked to dedicated monitoring programs.