We propose a matrix population modellingapproach in order to describe the dynamics of a grayling(Thymallus thymallus, L. 1758) population living in the Ainriver (France). We built a Leslie like model, which integrates theclimate changes in terms of temperature and discharge. First, weshow how temperature and discharge can be related to life historytraits like survival and reproduction. Second, we show how to usethe population model to precisely examine the life cycle ofgrayling : estimated numbers of individuals at the beginning ofthe reproduction season, estimated number of individuals insummer, comparison between observed and simulated numbers ofindividuals. Finally, we discuss our results in the framework ofthe assessment of impact of possible climate changes on graylingpopulations.