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Adipose Fin | Fly Casting Terminology
Adipose Fin
The adipose fin refers to a small, fleshy fin located on the back of certain species of fish, particularly salmonids. The adipose fin is found between the dorsal fin and the caudal (tail) fin, closer to the tail.
The adipose fin is unique because it does not have a specific functional purpose like other fins, such as the dorsal, pectoral, or caudal fins. Instead, it serves as an identifying characteristic of certain fish species, and its presence or absence can help anglers and fisheries scientists distinguish between different populations or species.
Many fisheries will clip the adipose fin on hatchery fish as they are released into the river system. Local fishing regulations may define harvesting limits based on the presence of lack of an adipose fin on any fish you catch. In many fisheries, fish with an intact adipose fin are required to be released—or extremely limited—as they are often part of conservation efforts to protect wild and genetically distinct populations. Anglers are often encouraged to handle these fish with care and release them unharmed to help maintain the sustainability of the fishery.
Not all fish have an adipose fin. In some species, such as trout, char, salmon, and steelhead, the adipose fin is commonly present. However, in other fish species, such as bass or pike, the adipose fin is absent.