Not so long ago, in watercourses not so far away, a war broke out between two Ponto-Caspian dreissenid bivalves. This large-scale conflict pits the zebra mussel, Dreissena polymorpha, against the quagga mussel, Dreissena rostriformis bugensis. If the first information available on the two species announced a disappearance of D. polymorpha in favor of D. bugensis, apparently better armed, the reality of the field is not so clear-cut. In this context of unclear invasion dynamics, the acquisition of new knowledge on the ecophysiological traits of these two species is therefore necessary. We propose here to review the knowledge acquired by our team on these two species in the Moselle basin. Although a decline in the abundance of D. polymorpha was observed, the species is still present, and an equilibrium between the two species has been reached. Reproduction is a key process in this conflict: the quagga mussel has a longer gamete emission period than the zebra mussel. This is also coupled by an energetic trade-off: the quagga mussel would allocate more energy to reproduction than to its stress tolerance, whereas the zebra mussel would have the opposite strategy. These divergent energetic needs are combined to different filtration and accumulation capacities of pollutants between the two species. In a context of global changes, the study of ecophysiological responses of invasive species could be a relevant way to better predict which side will awaken the force.