Approaches for the assessment of environmental impacts of contamination rely on toxic effects observed mainly at the individual level. These effects are then extrapolated to higher levels of biological organization (population, community and ecosystem) that constitute the protection goals of environmental regulations (REACH, WFD). Individual performance is governed by the allocation of energy to the physiological processes. DEB theory (Dynamic Energy Budget) formalizes the allocation of energy to key physiological functions (growth, maintenance and reproduction). However, until now, these models assume a permanent energy allocation to the reproduction during the lifespan of an organism, while it is generally a discrete process driven by physiological constraints. This is particularly true for crustaceans for which reproduction is synchronized with molt, such as Gammarus fossarum, a keystone species playing an important role in the functioning of European freshwater ecosystems. The aims of our presentation are (1) to present a mechanistic DEB model describing the allocation of energy during a reproductive cycle of G. fossarum females exposed to different temperatures and (2) to illustrate how it can be used under stress conditions. According to the knowledge on G. fossarum reproductive cycle, we schematized the biomass fluxes occuring during a reproductive cycle and formalized them by six differential equations. Considering different temperatures and different sizes of females allowed to consider different feeding rate values for the calibration of energetic processes implied during a reproductive cycle. Parameters were then estimated by Bayesian inference: we obtained precise estimations for the parameters. In particular, we estimated that females allocate 12% [0.11-0.14] of the assimilated energy to reproduction and predicted that 83% of the observations were within the predictive credible intervals. The model was then validated on other data. Finally, we fixed the scheme of energy allocation and compared the model predictions with lower food inputs to what is observed when females are under such food limited conditions. We showed that the more the food was restricted, the more the model underestimated reproduction, meaning that energy allocation was modified to privilege reproduction. Our study shows how a DEB formalism may describe the energy allocation processes of a crustacean for which reproduction occurs in a discrete way during successive molts.