What is "adipose fin"?

The adipose fin is a small, fleshy fin found on the back of some fish, positioned between the dorsal fin and the tail fin. Unlike other fins, the adipose fin does not have any bony structures or rays and consists primarily of adipose tissue. It is soft and lacks any known function related to movement or propulsion. The purpose of the adipose fin remains somewhat mysterious, but it is believed to have sensory functions, potentially serving as a sensory organ for detecting water pressure, vibrations, or other environmental cues. The adipose fin is found in various fish species, including salmon, trout, and catfish, and its presence or absence can be used as a distinguishing characteristic in identifying different fish species.