Overview on pathogenesis and histopathological observations of hyperostosis in two fish species; Scomberoides lysan (Forsskal, 1775) and Pomacanthus sextriatus (Cuvier, 1831) collected from El- Jubail province, Saudi Arabia

During years 2012 to 2018, two fish species, doublespotted queenfish ( Scomberoides lysan) and sixbar angelfish ( Pomacanthus sextriatus ) were regularly examined during filleting processing in fish markets at Jubail province, Saudi Arabia. The routine fish inspection of the fillet- by products (fish skeletons) of these two species showed prominent and frequent hard circumscribed ossified masses attached to the spines. In Scomberoides lysan 60% of the examined fishes were affected and the hyperosteoid overgrowths were noticed in both haemal and neural spines. In Pomacanthus sextriatus 10% showed nearly the same lesion but it was mainly observed in the neural spines. In gross examination, the swelling appeared very hard, round and smooth; the cut section showed grayish- white, granular, greasy and hard central contents. In histopathological examination, the hard masses showed hyperosteoid bony tissue with variable degrees of ossification surrounded with peripheral fibrous tissue capsule containing dilated lymph and blood vessels and accompanied with edema. The underlying tissue was a thick layer of acellular calcified bony tissue while the central area of the swelling was honeycomb in its appearance with cavities filled with blood and adipocytes together with golden brown pigments, hemosiderin. Our study concluded that hyperostosis occurs at high prevalence rates in S. lysan and P. sextriatus with characteristic histopathological lesions.