France is one of the major mussel producers in Europe with two commercially important species Mytilus edulis, and M. galloprovincialis. Since 2014, French mussel farms have been vulnerable to Abnormal Mussel Mortality (AMM) with mortality rates ranging from 30 to 100%, and varying spatially and temporally. One of the proposed factors influencing mortality is the haemocyte cytogenetic quality. The purpose of this study was to estimate the response to selection of cytogenetic quality trait using a divergent selection (DS) approach for the two important mussel species cultivated in France, and explore the relationship between the cytogenetic quality and survival using a cohabitation protocol with mussels sampled in a AMM site. In January 2022, wild mussels were sampled in Agnas and in Biarritz representing M. edulis and M. galloprovincialis, respectively. Their cytogenetic quality was measured using haemolymph by flow cytometry, and a DS was applied with 1.40 intensity of selection to produce contrasted groups (high/low) as well as control group in May/June 2022. The offspring cytogenetic quality was measured in June 2023. The response to selection after one generation of mass selection on the liability scale was 1.44% for M. edulis and null for M. galloprovincialis. Mortality of high, low and control groups for each species was recorded using a cohabitation experiment from March-October 2023. In October 2023, high mortality was recorded for hatchery-produced mussels (77%), with no significant difference between species, as well as within species between the high, low and control groups. Furthermore, a non-significant from zero phenotypic correlation was observed between cytogenetic quality and survival of offspring. Nevertheless, further investigations are required to validate the genetic basis of the cytogenetic quality of the mussel species cultivated in France