The effect of starvation on gonad morphology and egg production of Calanus finmarchicus was studied during the winter spring transition in a North Norwegian fjord. Single females were exposed either to surplus food or to filtered seawater for 4-9 d in short-term experiments and for 3 weeks in long-term experiments. Additional laboratory experiments were performed with female C. finmarchicus from the Norwegian Sea, studying the resumption of egg production after short (1-3 d) or long (15 d) intervals of starvation. In Fed females, gonads were mature and rates of egg production were relatively high. During starvation, gonads remained immature or returned to an immature stage; no eggs were produced. Histological analysis of starving females showed that oocytes in the diverticula disintegrated, while cells in the ovary were intact. After two weeks of starvation, reproductive activity resumed within a week of surplus feeding. However, egg production remained significantly lower than in females fed continuously. When Female C. finmarchicus were exposed to short starvation intervals, reproduction decreased significantly owing to both higher percentages of non-spawning females and decreasing clutch sizes. The experiments have shown that starvation periods have a strong influence on reproduction of C. finmarchicus, which was dependent on the duration of starvation and the timing within the maturation cycle. Lifetime fecundity is probably considerably reduced, obviously during starvation but also as a result of long-term effects. © 2000 International Council for the Exploration of the Sea.