The adipose fin is a small, fleshy fin found on some species of fish, typically located between the dorsal fin (on the back) and the tail fin. This fin is soft and lacks the stiff rays found in other fins. The term “adipose” refers to fatty tissue, and the adipose fin is so named because it often contains a small amount of fatty tissue.
The presence of an adipose fin is particularly notable in certain types of salmonids, such as salmon and trout. In these species, the adipose fin is commonly used as a distinguishing feature to identify hatchery-raised individuals from wild ones. Fisheries management programs often involve the removal of the adipose fin (adipose fin clipping) in hatchery-raised fish before they are released into the wild. This practice helps researchers and anglers easily recognize and differentiate between wild and stocked fish.
While the specific functions of the adipose fin are not fully understood, it is generally believed to play a role in maintaining stability during swimming. In some fish species, the adipose fin may have additional sensory functions or contribute to their overall agility in the water.