finlets

Finlets may reduce turbulence for high-efficiency swimmers

Finlets are highly specialized fins located on the dorsal and ventral sides of the body between the dorsal fin and/or the anal fin and the caudal fin.  They are only found on certain fish including those in the Scombrid family (mackerels, tunas, and bonitos), Scomberesocid family (sauries), snake mackerels (family Gempylidae), and Bichirs (family Polypteridae).  For Bichirs, the finlets are only on the dorsal side and they take the place of a traditional dorsal fin.  For Scombrids and Scomberesocids, finlets are small, rayless, non-retractable fins located on both the dorsal and ventral margins of the body.  Finlets in Scombrids have been evaluated for their contribution to locomotion because these fish are such high-performance swimmers.  Finlets may contribute to dampening of cross-flow turbulence around the caudal peduncle.

Finlets are found behind dorsal and anal fins