Basal expansion of anal‐fin rays: a new osteological character in weakly discharging electric fish (Mormyridae)

Bone expansion of anal‐fin rays in mormyrid fish is introduced as a new osteological character to distinguish two mormyrid species, Brienomyrus brachyistius from Nigeria and Brienomyrus kingsleyae from Gabon. This character is sexually dimorphic and species‐specific, affecting the bases of anal‐fin rays in adult males only. Between the two species, it differed in degree, the number of rays involved, and the number of the first ray affected. These differences together with differences in conventional meristic and morphometric characters further support ongoing revisions of Brienomyrus taxonomy.