Prevalence of haemic neoplasia in cockles and cohabiting bivalve species on the western coast of France and the southern coast of Portugal

Haemic neoplasia is a cancer affecting several bivalve species and has become transmissible in some lineages. This study assesses its prevalence in common cockles (Cerastoderma edule) along the western coast of France and the southern coast of Portugal, regions with important bivalve fisheries. Cockles and cohabiting bivalve species (Ruditapes spp. and Scrobicularia plana) were sampled across multiple locations, and haemic neoplasia was diagnosed through cytological analysis. In the Algarve, a decline in prevalence was observed between 2017 and 2024, while in Normandy, the disease was detected for the first time. No cases of haemic neoplasia were found in the cohabiting clam species, suggesting that cockle cancer transmission may be species-restricted. Morphometric analyses revealed no significant differences in size or mass between affected and non-affected cockles, indicating that external traits are not reliable indicators of infection. These findings expand knowledge on the geographical distribution of haemic neoplasia and highlight the need for continued monitoring to assess potential changes in its prevalence and impact on bivalve populations. This article is part of the theme issue 'Managing infectious marine diseases in wild populations'.