Monitoring the adverse effects of environmental contaminants, and especially wastewater effluents, on the reproduction of species from diverse taxa of biodiversity is an ongoing challenge in ecotoxicology. In this context, a chronic sub-lethal toxicity test was developed on Gammarus fossarum, a keystone species of European freshwater ecosystems, to detect adverse outcomes (such as endocrine disruption) of the exposure to chemical compounds. Moreover, protocols were developed for in situ bioassays with transplanted caged G. fossarum to diagnose toxicity in freshwater systems. Such field bioassays permit to control biotic factors known to influence endpoints measurements, but the impact of abiotic factors like water temperature and hardness can not be controlled. In previous laboratory ecophysiological studies, we shown that the moulting cycle of G. fossarum only depends on temperature. A temperature-dependent model was thus developed to describe the moulting development of G. fossarum according to water temperature. The aim of our presentation will be to show how we can use such a model to take into account the effects of temperature in the interpretation of responses measured during in situ assays. Based on ex situ and in situ case studies, we will firstly show the improvement of the the temperature-dependent model by transplanting gammarids throughout four seasons in two reference stations. Secondly, to illustrate the relevance of this model in interpreting the moulting development modulation of G. fossarum exposed to wastewater effluents, we will show the results from: 1- ex situ exposure performed to assess toxicity reduction by alternative tertiary treatments in pilot WWTP; 2- in situ exposure upstream and downstream from three WWTP effluent outputs discharged in Rhône-Alpes Rivers (France). Our study underlined the relevance of formalizing the impact of confounding factors on the responses of ecophysiological tests in order to have a good interpretation of in situ bioassays. Furthermore, the reproductive bioassay with caged G. fossarum appeared as a relevant tool to diagnose toxicity of wastewater effluents with potential adverse effect for reproductive processes within receiving ecosystems.