Cod Scale
まだらのウロコ [madara no uroko] or 'speckled scale'. Note that 'madara' (in this case written マダラ) can also mean 'Pacific cod', which is where the English name of the item comes from.
Grimoire of the Rift

Buy: - (sell: 300 gil)
Use: Arch Sword, Lohengrin, Trident
Reward: The Way of the Timid (once), Plea for Help x2 (once)
Type: Bone, Rank: ★
Description: These brown, speckled scales are used in a surprising number of goods.
Final Fantasy Tactics S

Buy: - (sell: 50 gil)
Use: Knuckles, Mace
Obtain: Nation of Magick Nensa-Ramoi/Forest of Sand Pillars
Description: A somewhat uncommon bone
Category: Item