finlet

from The Century Dictionary.

• noun A little fin.
• noun Technically, in ichthyology, detached rays of a dorsal or anal fin, forming a kind of fin, especially in the mackerel family. See Scombridæ.

from the GNU version of the Collaborative International Dictionary of English.

• noun A little fin; one of the parts of a divided fin.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun ichthyology Small rayless non-retractable fins between the last dorsal or anal fin and the caudal fin of some fishes.