Hyperostosis is described as a productive change in bone tissue, characterized by an increase of the periosteal ossification combined with resorption of the bony tissue (Meunier et al., 2010). Hyperostosis was described for the first time as “os vormianum” by Worm in 1655 (see Schlüter et al., 1992). In 1881 Van Beneden reported hyperostosis in fish bones as a “corps énigmatiques” (Schlüter et al., 1992), and in 1982, it was described by Grabda (1982) as “like cystic growths.” Hyperostosis occurs in specific bones that show thickening, which develops into a swollen structure. Among bony elements that have shown hyperostosis in teleost fishes are pterygiophores, skulls, claviculae, and hemal and neural spines (Smith-Vaniz et al., 1995).
The occurrence of swollen or hyperostotic bones has been identified in a wide range of fish species belonging to about 22 (see Smith-Vaniz et al., 1995; Smith-Vaniz and Carpenter, 2007; Rapisarda et al., 2008; Meunier et al., 2010; Giarratana et al., 2012). Hyperostosis can also be used to help distinguish between closely related species, such as Pagrus major and Chrysophrys auratus (Yasuda and Mizuguchi, 1969).
Hyperostosis has not been reported previously from any fishes from Oman. However, Klausewitz (1965) reported on the presence of hyperostotic skull bones in Pomadasys hasta collected from the Red Sea, which the nearest area to Oman.
In this study, the gross morphology of the hyperostotic bones in the concertina fish, Drepane longimana (Drepanidae), the striped piggy, Pomadasys stridens (Haemulidae), and the longfin batfish Platax teira (Ephippidae) are described.
This study is based on one specimen each of Pomadasys stridens (326 mm TL, 314 mm SL), Drepane longimana (450 mm, TL, 440 mm SL), and Platax teira (660 mm TL, 650 mm SL) captured off the coast of Muscat City using a deep gill net on 25 May 2012. The specimens were numbered, measured to the nearest mm, weighed to the nearest g, and radiographed. For each specimen, two or three radiographic images were necessary to encompass the entire length of the fish. After the specimens were radiographed, their skeletal deformities were documented, especially including the length of the major and minor axes of each deformity.
The hyperostotic regions of the three species in question are present on the neural and hemal spines and the dorsal fin pterygiophore. In Pomadasys stridens there are four hyperostotic neural spines of caudal vertebrae 3–6. The hyperostosis varies in size, shape, and position on the spine (Fig. 1). The hyperostotic regions range in length between 2.6 and 7.8 mm. The largest hyperostotic bone is that of the neural spine of the fourth caudal vertebra and the smallest is that of the sixth caudal vertebra. The shapes are irregular-spherical, pear-shape, and spherical for the third, fourth, and fifth – sixth caudal vertebrae, respectively. The four hyperostotic regions are situated in descendent positions on the neural spines of the caudal vertebrae, with the third bone being the highest (Fig. 1).
In Drepane longimana, the hyperostosis is present on the neural and hemal spines of the ninth caudal vertebra and on the hemal spine of the 12th caudal vertebra (Fig. 2). Those of the ninth vertebra are spherical in shape while that of the 12th vertebra is oblong in shape. All three hyperostotic regions are situated in the same position on the neural and hemal spines, with that of the 12th vertebra being the largest. The hyperostotic regions range in length between 15 and 22.5 mm (Fig. 2).
In Platax teira, the six hyperostotic regions are situated as follows: on the first dorsal-fin pterygiophore; on the neural and hemal spines of the first caudal vertebra; on the neural spine of the third caudal vertebrae; on the neural and hemal spines of the fifth caudal vertebra; and on the hemal spine of the seventh caudal vertebra (Fig. 3). The largest of the seven hyperostotic regions are those of the pterygiophore and the hemal spine of the first caudal vertebra, whereas the smallest regions are those of the neural spine of the fifth caudal vertebra and the hemal spine of the seventh caudal vertebra. The regions range in width between 18.4 and 46 mm and in length between 23 and 82 mm. The shape of the hyperostotic regions varies from spherical to pear shape.
Except for the hyperostotic region of the hemal spine of the first caudal vertebra, which is located on the tip of the spine, the remaining six regions are located in the distal halves of the lengths of the neural and hemal spines.
Hyperostosis is present in several groups of vertebrates, including fishes (Capasso, 2005), where it has been used by archeologists and fish systematists as a diagnostic criterion and as a taxonomical tool, respectively.
Smith-Vaniz et al. (1995) reported on the presence and distribution of hyperostosis in fishes. The size, shape, and position of the hyperostotic bones revealed in the three fish species reported on herein are comparable with those given by Smith-Vaniz et al. (1995).
The results of this study support this suggestion. The shapes of the hyperostotic bones of the three species in question are distinctive from one another. Those of P. stridens are spherical; those of D. longimana are pear-shaped, and those of P. teira are oblong to irregular-shaped.
Hyperostosis is considered as a non-pathological formation by several authors (Olsen, 1971; Desse et al., 1981; Gauldie and Czochanska, 1990; Smith-Vaniz et al., 1995). The most acceptable reason to not consider hyperostosis as a pathological condition is that it is a species-specific characteristic. Furthermore, the predictable ontogenetic expression of these structures in fish species disproves the hypothesis that it is a disease.
Since only a single specimen was obtained for each of the three Omani species, it is not possible to test the hypothesis of Capasso (2005) in correlating fish size (total length and weight) and number of hyperostotic bones found in each specimen to increase body weight to facilitate bottom browsing.