First record of hyperostosis in channel scabbardfish <i>Evoxymetopon taeniatus</i> Gill, 1863: An mesopelagic migratory fish

The majority of records of hyperostosis in the literature are from highly active tropical species found in shallow waters, with information about hyperostotic deep-sea fish being scarce. This study describes the occurrence of hyperostosis, a skeletal anomaly, in two specimens of channel scabbardfish Evoxymetopon taeniatus Gill, 1863, obtained from two different regions in Rio de Janeiro, Southeast Brazil. Through radiographic image analysis, the presence of hyperostosis was observed in two distinct bone regions: dorsal pterygiophores (DPT) and anal pterygiophores (APT), affecting a significant number of bones: DPT-83 of 87 (95.40%) and 40 of 85 (40.06%) and APT-55 of 55 (100%) and 23 of 54 (42.59%) for the largest and smallest collected individuals, respectively. Histological analyses of the DPT and APT affected by the condition revealed high porosity in the bone tissue, with a high number of vascular channels commonly reported during hyperostosis. This is the first report of hyperostosis in channel scabbardfish, a mesopelagic fish with rare sightings and characterized by its vertical migrations.