Hyperostosis in Fishes: An Update With New Species Records

ABSTRACT Literature reports of hyperostosis are often misleading and have been confused with osteomas, a pathological condition. Hyperostotic bones are known to occur only in bony fishes of the class Actinopterygii, within at least 16 orders, 35 families, 89 genera, and 153 species. They are present almost exclusively in marine fishes and exceptionally in a few extinct freshwater species known from hypersaline environments and one extant cichlid. Hyperostosis is best represented in the family Carangidae where it is known to occur in 53 of approximately 181 valid species. We also provide a synthetic report on what we know and what misconceptions exist regarding hyperostosis. Patterns of hyperostosis are often species‐specific but provide no useful phylogenetic information. In species known to develop hyperostosis, it is usually not apparent (non‐histologically) in juveniles and typically only becomes fully developed in the largest individuals. The timing of hyperostosis on‐set in different bones is often sequential rather than simultaneous across different bones. Most marine Neoteleostei have acellular skeletons but histological observations have shown that in species exhibiting hyperostosis, areas of active remodeling are composed primarily of cellular bone characterized by a rich vascular network and bone‐resorbing osteoclasts. Hyperostosis is an enigmatic dimension of diversity in the anatomy of fishes. This excessive overgrowth of bone is natural in origin, occurs almost exclusively in marine fishes, is generally species‐specific, and becomes fully developed only in large individuals. We document hyperostosis in 35 families, 89 genera, and 153 species. We also present an extensive literature review and radiographs of selected species.