Ganoine Explained

Ganoine or ganoin is a glassy, often multi-layered mineralized tissue that covers the scales, cranial bones and fin rays in some non-teleost ray-finned fishes,^[1] such as gars and bichirs, as well as lobe-finned coelacanths.^[2] It is composed of rod-like, pseudoprismatic apatite crystallites, with less than 5% of organic matter.^[3] Existing fish groups featuring ganoin are bichirs and gars, but ganoin is also characteristic of several extinct taxa.^[4] It is a characteristic component of ganoid scales.

Ganoine is an ancient feature of ray-finned fishes, being found for example on the scales of stem group actinopteryigian Cheirolepis.^[4] While often considered a synapomorphic character of ray-finned fishes, ganoine or ganoine-like tissues are also found on the extinct acanthodii.^[4]

It has been suggested that ganoine is homologous to tooth enamel in vertebrates^[1] or even considered a type of enamel.^[3] Ganoine indeed contains amelogenin-like proteins^[1] and has a mineral content similar to that of tetrapod tooth enamel.^[5]

Notes and References

1. Zylberberg . L. . Sire . J. -Y. . Nanci . A. . 10.1002/(SICI)1097-0185(199709)249:1<86::AID-AR11>3.0.CO;2-X . Immunodetection of amelogenin-like proteins in the ganoine of experimentally regenerating scales of Calamoichthys calabaricus, a primitive actinopterygian fish . The Anatomical Record . 249 . 1 . 86–95 . 1997 . 9294653 . free .
2. Sire. Jean-Yves. Donoghue. Philip C. J.. Vickaryous. Matthews K.. Origin and evolution of the integumentary skeleton in non-tetrapod vertebrates. Journal of Anatomy. en. 214. 4. 409–440. 10.1111/j.1469-7580.2009.01046.x. 0021-8782. 2736117. 19422423. 2009.
3. Bruet . B. J. F. . Song . J. . Boyce . M. C. . Ortiz . C. . 17288901 . Materials design principles of ancient fish armour . 10.1038/nmat2231 . Nature Materials . 7 . 9 . 748–756 . 2008 . 18660814. 2008NatMa...7..748B .
4. Richter . M. . A microstructural study of the ganoine tissue of selected lower vertebrates . 10.1006/zjls.1995.0023 . Zoological Journal of the Linnean Society . 114 . 2 . 173–212 . 1995 .
5. Book: Ørvig, T.. Structural and Chemical Organization of Teeth. Phylogeny of tooth tissues: Evolution of some calcified tissues in early vertebrates.. 1967. Academic Press. New York. 45–110.