Fulcra are peculiar bony flaps behind the dorsal fin of sturgeons that form the dorsal keel of the caudal fin.
For example, in Sterlet, behind the dorsal fin begins a series of arch-shaped bony flaps called fulcra, which form the dorsal keel of the caudal fin and gradually develop into bony rays, lepidotrichia, which support the dermal blade of the caudal fin.
Fulcra
Tags: fulcra