1) Fish-scale covering 2) Ganoin 3) Secretion 1) Ganoin 
Ganoine or ganoin is a glassy, often multi-layered mineralized tissue that covers the scales, cranial bones and fin rays in some basal ray-finned fishes. It is composed of rod-like, pseudoprismatic apatite crystallites, with less than 5% of organic matter. Existing fish groups featuring ganoin are bichirs and gars, but ganoin is also characteristi...
• (n.) A peculiar bony tissue beneath the enamel of a ganoid scale.
Ga'no·ine noun (Zoology) A peculiar bony tissue beneath the enamel of a ganoid scale.