Mormyrids are soft-rayed bony fishes with abdominal pelvic fins, forked tail fins, small mouths and eyes, restricted gill openings, and small scales.
Subsequently infected cod developed chronic infections with clinical signs such as petechial haemorrhages and ulcerations on the ventral abdominal wall, in addition to fin erosion.
The ventral fins are abdominal; the caudal fin is truncate.
Vertebral count data were extrapolated from scale-row counts in fossil forms, with the anterior insertion of the anal fin corresponding to the abdominal – caudal transition.
Rather, dissociation between the anus/osteological boundary between the abdominal and caudal regions and the anterior insertion of the anal fin [ 27, 35, 36] is observed such that a posterior shift in the dorsal and anal fins may occur without a change in the number of abdominal vertebrae.
The preferential addition of abdominal vertebrae fits with the previously hypothesized existence of a patterning module consisting of the boundary between the abdominal and caudal vertebral regions, and the anterior insertion of the anal fin.
More detailed study of both fossil and recent species is needed to assess whether the ratio of abdominal to caudal vertebrae is correlated with variable displacement of the anal fin in Sphyraenidae.
The preferential addition of abdominal vertebrae in fishes with an elongate body shape is consistent with the existence of a conservative positioning module formed by the boundary between the abdominal and caudal vertebral regions and the anterior insertion of the anal fin.
The observed tendency to add abdominal vertebrae as a mechanism driving axial elongation in fishes with the 'ambush predator' body shape is consistent with the existence of a conserved positioning module involving the association of the boundary between the abdominal and caudal vertebral regions, the anus, and the anterior insertion of the anal fin [ 26].
The anus is generally, but not exclusively [ 27], located at the end of the body cavity at the boundary between the abdominal and caudal vertebral types, and constrains the anteriormost point of insertion of the anal fin pterygiophores.
