The adipose fin is a small fleshy fin found posterior to the dorsal fin and anterior of the caudal fin.  It is only found on few fish, including trout, salmon, and catfish.  When it was named, it was thought to hold fat, or adipose, tissue.  Once this hypothesis was disproved, fisheries biologists long considered this fin to be “non-functional.”  More recently, research suggests that the adipose fin may serve as a “precaudal flow sensor” to improve maneuverability in turbulent waters. 

The adipose fin may serve as a “precaudal flow sensor”

 This new research may raise concerns because adipose fin clipping is commonly used to “tag” hatchery reared salmon to distinguish them from wild salmon for catch and release management purposes. (fishionary.fisheries.org/adipose-fin)

For more information on the adipose fin, please visit: http://thefisheriesblog.com/2013/05/28/the-adipose-fin-old-mysteries-with-new-answers/